Magnetically suspended and rotated rotor

ABSTRACT

The impellor of a blood pump is supported by permanent magnets on the impellor and pump housing and stabilized by an electromagnet on the housing. A control circuit supplies current to the electromagnet to maintain the axial position of the impellor at a control position in which the impellor is in mechanical equilibrium under permanent magnet forces and static axial forces on the impellor to minimize energy consumption in the support of the impellor. The impellor is rotated magnetically and stator coils in the housing are supplied with electric currents having a frequency and amplitude adjusted in relation to blood pressure at the pump inlet to match the flow characteristics of the pump to physiological characteristics of the natural heart. A cavity is formed in the impellor to match the average specific gravity of the impellor and portions of the suspension and drive systems thereon to the specific gravity of blood to further minimize power consumption by the pump. A valve member can be formed on the impellor to mate with a restriction in the pump inlet for pumps used to assist the pumping action of the natural heart.

This application is a continuation of Ser. No. 914,486, filed Oct. 2,1986, entitled "MAGNETICALLY SUSPENDED AND ROTATED ROTOR" now abandoned,which is a continuation of Ser. No. 720,081, filed Apr. 4, 1985,entitled "MAGNETICALLY SUSPENDED AND ROTATED ROTOR" now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates generally to apparatus for suspending androtating rotors and, more particularly, but not by way of limitation, tothe suspension and rotation of the impellors of pumps that can beimplanted in the human body for replacing or assisting the natural heartin the pumping of blood through the circulatory system.

It has long been a goal of experimenters to develop a pump which canserve as an artificial heart and a variety of types of pumps have beendesigned to either replace or assist the natural heart in its functionof pumping blood through the human body. While these prior art pumpshave met with some degree of success, a number of problems associatedwith them have remained unsolved so that a practical artificial hearthas not previously been developed. For a pump to be usable as areplacement or as an assist for the human heart, the pump must meetcertain practical requirements which have been discussed in U.S. Pat.application Ser. No. 245,007, the teachings of which are herebyspecifically incorporated herein by reference.

On a general level, the requirements for a blood pump are that it mustnot cause substantial injury to the blood and it must not require alarge back-up system for its operation. Injury to the blood wouldpreclude use of the pump over extended periods of time that would berequired, for example, if the pump were to be a replacement for thenatural heart or an assist that is to be implanted for the life of thepatient. The size of the back-up system is a requirement that relates tothe quality of life; for a pump to be practical, it must not requirethat the recipient be forever tied to an immobile life support system.

The requirement that the pump not require a large back-up system placescertain technical requirements on the construction of a practical bloodpump. One such requirement is that the pump be operable electrically sothat the power supply for the pump can be provided by rechargeablebatteries. At present, the technology is available to implant batterieswithin the human body and to recharge these batteries periodically usingan induction coil that can be placed against the body as has been notedin the aforementioned U.S Pat. application Ser. No. 245,007. Similarly,it is presently possible to build highly efficient, electricallyoperated pumps in which the pumping action is achieved by the rotationof an impellor to cause a liquid to be driven through a chamber in whichthe impellor is located The problem that has not been solved prior tothe present invention is to provide such a pump which will not causeunacceptable injury to blood.

A pump can injure blood in several ways. If the impellor of the pump issupported by mechanical bearings in contact with the blood, relativemovement between parts of the bearings can result in excessivemechanical working of the blood causing blood cells to rupture Glandswhich might be used to seal these bearings cannot solve this problem.Since the impellor will be moving with respect to the gland, blood inthe neighborhood of the gland-impellor interface will be subjected tohigh sheer stresses and friction which can cause the rupture of bloodcells in much the same manner that rupturing of blood cells isoccasioned in a bearing.

Another mechanical effect that can injure blood is the formation ofregions within the pump in which the blood is stagnant or in whicheddies without sufficient blood exchange, equivalent to stagnation, mayoccur. Stagnation tends to result in coagulation of the blood.

A third effect that can injure blood is excessive heating as the bloodpasses through the pump. If the pump is inefficient, so that a largepart of the energy supplied to the pump appears as heat discharged intothe blood, blood cells may be damaged through overheating or coagulationof the blood may occur. In this regard, it should be noted that albumenbegins to denature at 42° C. so that inefficiency of the pump resultingin overheating of the blood can be a serious problem.

SUMMARY OF THE INVENTION

The present invention solves the problems that have been encounteredwith earlier blood pumps through a novel approach to rotor suspensionand rotation, an approach which leads not only to a practical blood pumpbut additionally provides an apparatus which, it is contemplated, willhave a variety of practical applications in a number of fields. Thus,the rotor can be the impellor of a pump and, more specifically, a bloodpump that can be implanted in the body to replace or assist the naturalheart. However, the invention is not limited to such use; rather, in itsmost general form, the invention is an apparatus for suspending androtating a rotor for any useful purpose. For example, it is contemplatedthat the rotor might be the impellor of a pump that is used to pumpradioactive, abrasive, or corrosive fluids, liquids containing dissolvedgases, or the rotor of a gyroscope in a missile guidance system wherepower requirements play a role or any suspended rotor in an accelerated,moving system in general.

Nevertheless, it will be useful to consider the apparatus of the presentinvention in a specific context to fully bring out the benefits andadvantages the invention provides. It is in this spirit of completedisclosure that the apparatus will be described with particularreference to the application in which the invention is particularlyadapted to the pumping of blood through the human body.

As adapted for use as a blood pump, the apparatus of the presentinvention solves the problems that have been encountered with earlierblood pumps by providing a pump having an impellor that is magneticallysuspended in a housing and magnetically rotated to effect the pumping ofblood through the housing. Since the impellor is magnetically suspendedand rotated, no bearings which might mechanically damage blood areneeded in the pump and no bulky back-up system is needed to operate thepump. Rather, a battery pack can be utilized for this purpose. Moreover,the apparatus is constructed so that very little energy is expended ineffecting the suspension of the impellor with the result that dischargeof heat into the blood from the magnetic suspension system is held to aminimum level. An advantage of this construction is that the low powerconsumption needed to effect the suspension of the impellor enables abattery pack which can be used to operate the apparatus to be implantedin the body and periodically recharged as has been noted above. Thus,the present invention provides a heart replacement or assist that iscapable not only of preserving the life of the user but one which willmake that life meaningful by providing only minimal interference withthe user's conduct of normal human affairs.

Additionally, the magnetic suspension of the impellor solves problemsassociated with pump lifetime. A severe problem that has beenencountered with prior art pumps is wear and embrittlement of materialof which the pumps are constructed and, in the case of blood pumps, wearand embrittlement of blood compatible materials that are included in theconstruction of the pumps. Both wear and embrittlement cause pumpfailure or changes in the surface structure of blood compatiblematerials, reducing the effectiveness of such materials, requiringtermination of the use of the pump. The use of a magnetic bearing tosupport the impellor eliminates stresses that might otherwise be exertedon the materials, including blood compatible materials, of which thepump might be constructed. (A preferred construction of the pump of thepresent invention, when used as a blood pump, is the utilization ofrigid substrates coated with a blood compatible material. An importantadvantage the magnetic suspension of the impellor of the presentinvention is that it permits all surfaces in contact with blood to becomposed of materials which need not have special properties, such asflexibility, that are not associated with compatibility.) Thus, themagnetic suspension of the rotor eliminates bending stresses, frictionalforces, and heating stresses to provide the pump with maintenance free,substantially indefinite lifetime.

To provide the pump adaptation of the apparatus with the capability ofmeeting these ends, the support of the impellor is effected by permanentmagnets that are located on the impellor and the housing within whichthe impellor is rotated. Since the forces these magnets exert on theimpellor to support it are conservative forces, the support of theimpellor requires no expenditure of energy which might be degraded intoheat and discharged into the blood to possibly cause injury to theblood. Rather, the only expenditure of energy required in the suspensionof the impellor is energy used to stabilize the impellor suspensionsystem and such energy expenditure can be minimized by supporting theimpellor at a control position at which the impellor is in mechanicalequilibruim.

It is well known that a suspension system comprised solely of permanentmagnets cannot be stable so that no object can be supported solely bypermanent magnets, a fact that is based on Earnshaw's theorem. However,the instability in the suspension of an object by permanent magnets issubject to control. That is, permanent magnets can be used to stablysupport an object with respect to some, but not all, degrees of freedomof movement of the suspended object about a selected support positionand the degree of freedom for which the suspension is unstable can beselected. The present invention exploits this selection capability toprovide a suspension system for a pump impellor that maximizes permanentmagnet support forces while requiring very little energy to maintain theimpellor in position in the pump housing, thereby minimizing thegeneration of heat by the suspension system to enable the pump to beused as a replacement for, or an assist to, the natural human heart inthe pumping of blood through the circulatory system. Such powerminimization also permits the use of much smaller components in a pumpand the use of a highly portable power supply for the pump.

In the pump of the present invention, the permanent magnets are mountedon the pump impellor and on the pump housing and the magnetization ofthese permanent magnets is selected so that the permanent magnets willtend to align the rotation axis of the impellor with a selected supportaxis on the housing. With such selection, the permanent magnets will notstably support the impellor with respect to axial movement of theimpellor along the housing support axis. Rather, the permanent magnetswill tend to drive the impellor away from a null position on the housingsupport axis at which the permanent magnet forces cancel. Anelectromagnet is then provided, along with an electromagnet controlcircuit that controls the current through the electromagnet inaccordance with impellor position, to exert axial forces on the pumpimpellor, via portions of the permanent magnet assembly mounted on thepump impellor, so that the electromagnet can be used to overcome theaxial instability in the support of the impellor by the permanent magnetassembly. Since the electromagnet is used only to overcome theinstability, as opposed to providing support for the impellor, verylittle power is required to operate the electromagnet. Moreover, and aspracticed in one preferred embodiment of the invention, the currentthrough the electromagnet can be continuously monitored and control ofthe current can be effected to maintain power consumption by theelectromagnet at a minimum in the presence of static, or long term,axial forces on the impellor in addition to the forces arising from thepermanent magnets and the electromagnet of the impellor suspensionsystem. In the presence of static axial forces, the electromagnet drivesthe impellor toward a control position which is shifted slightly fromthe null position defined by the permanent magnets of the suspensionsystem so that the static axial forces are balanced by a force providedby the permanent magnets of the suspension system. The invention thusprovides, by way of example, flexibility in pump construction byenabling the permanent magnets of the suspension system to be used tocounteract reaction forces on the impellor that occur as the result ofpumping for certain pump designs.

In a pump constructed using the apparatus of the present invention,rotation of the impellor to pump blood is effected magnetically byconstructing the pump impellor such that the impellor serves as therotor of an electric motOr. In one preferred construction of theimpellor, a shorting ring is formed about the periphery of the impellorand stator coils are mounted in the pump housing about the shorting ringso that the pump impellor is also the rotor of an eddy current inductionmotor. Thus, no mechanical connections need be made to the pump impellorto suspend and rotate the impellor so that construction of a blood pumpfollowing the teachings of the present invention eliminates any need forbearings, glands and the like in contact with blood which could causemechanical damage to the blood. Additionally, the stator coils andshorting ring are placed in the pump so that the rotation of theimpellor produces, at most, only negligible forces on the impellor thatwould have to be overcome by the magnetic suspension system of theimpellor.

Another aspect of the present invention is the control of currentthrough the stator coils that are provided to rotate the impellor of thepump. In the natural heart, a relationship known as the Frank-Starlingeffect exists between the flow rate of blood through the heart and theblood pressure at the inlet to the heart. The present inventioncontemplates the control of current supplied to the stator coils that,with the impellor, form an electric motor so that the pump of thepresent invention mimics the Frank-Starling effect of the natural heart.Such control can readily be adapted to provide for rotor speed controlin accordance with a selected relationship to a selected measurablequantity in any application of the invention.

An important object of the present invention is to provide a rotorsuspension and rotation apparatus which can be adapted to a variety ofpractical applications.

Another important object of the present invention is to provide a pumpwhich can be implanted in the human body to provide a replacement for,or an assist to, the natural heart in the pumping of blood through thecirculatory system.

Another object of the invention is to provide a blood pump which doesnot require a large back-up system that would interfere with the freedomof movement of a person in which the pump is implanted.

Another object of the invention is to provide a blood pump which ishighly energy efficient so that damage to blood through discharge ofheat into the blood is substantially eliminated.

Another object of the invention is to provide an energy efficient rotorsuspension and control system that can be readily adapted to a varietyof pump designs without loss of efficiency.

A further object of the invention is to provide an apparatus thateliminates the need for glands and bearings in pumps.

Another object of the invention is to provide a pump that avoids flexingand frictional engagement of moving parts.

Yet another object of the invention is to provide an apparatus forsuspending and rotating a rotor in which the rotor speed can becontrolled in accordance with the value of a selectable physicalquantity.

Other objects, features and advantages of the present invention willbecome clear from the following detailed description of the inventionwhen read in conjunction with the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a pump, suitable for use as animplantable blood pump, constructed to employ the magnetic rotorsuspension and rotation apparatus of the present invention.

FIG. 2 is a cross section of the pump shown in FIG. 1 taken along line2--2 of FIG. 1.

FIG. 3 is a cross section of the pump shown in FIG. 1 taken along line3--3 of FIG. 1.

FIG. 4 is a cross section of the magnets of the magnetic suspensionsystem of the present invention illustrating the placement andmagnetization of the permanent magnet assembly of the suspension system.

FIG. 5 is a graphical representation of the axial component of permanentmagnet forces on the impellor of the pump shown in FIG. 1.

FIG. 6 is a graphical representation of the radial component ofpermanent magnet forces on the impellor of the pump shown in FIG. 1.

FIG. 7 is a graphical representation of the axial component of the totalforce on the impellor in the presence of a static, axial force on theimpellor.

FIG. 8 is a block diagram of the electromagnet control circuit for thepump impellor.

FIG. 9 is the circuit diagram of the astable multivibrator of theelectromagnet control circuit.

FIG. 10 is the circuit diagram of the IR transmitter of theelectromagnet control circuit.

FIG. 11 is the circuit diagram of one of the IR receivers of theelectromagnet control circuit.

FIG. 12 is the circuit diagram of the difference amplifier of theelectromagnet control circuit.

FIG. 13 is a circuit diagram for the integrator of the electromagnetcontrol circuit.

FIG. 14 is a circuit diagram of the sample and hold of the electromagnetcontrol circuit.

FIG. 15 is a circuit diagram of the timing circuit of the electromagnetcontrol circuit.

FIG. 16 is a circuit diagram for controller number 1 of theelectromagnet control circuit.

FIG. 17 is a circuit diagram for controller number 2 of theelectromagnet control circuit.

FIG. 18 is a circuit diagram of the power amplifier of the electromagnetcontrol circuit.

FIG. 19 is a graphical representation of the electrical characteristicsof the power amplifier shown in FIG. 18.

FIG. 20 is a timing diagram illustrating the operation of the timingcircuit of the electromagnet control circuit.

FIG. 21 is an isometric view of one preferred arrangement of statorcoils used to rotate the impellor of the pump shown in FIG. 1.

FIG. 22 is a block circuit diagram of a rotation control circuit used toprovide a current through the stator coils shown in FIG. 21.

FIG. 23 is a block diagram of the encoder of the rotation controlcircuit shown in FIG. 22.

FIG. 24 is a circuit diagram of the oscillator of the rotation controlcircuit shown in FIG. 22.

FIG. 25 is a circuit diagram of the modulator of the rotation controlcircuit shown in FIG. 22.

FIG. 26 is a graphical representation of an optimal operatingcharacteristic of the impellor of the pump shown in FIG. 1.

FIG. 27 is a side elevational view of a modified impellor for the pumpshown in FIG. 1.

FIG. 28 is an end elevational view of the impellor shown in FIG. 27.

FIG. 29 is a cross section in side elevation of another modification ofthe impellor of the pump shown in FIG. 1.

FIG. 30 is a cross section in side elevation of yet another modificationof the impellor of the pump shown in FIG. 1.

FIG. 31 is a cross section in side elevation of a second embodiment of apump employing the magnetic rotor suspension and rotation apparatus ofthe present invention.

FIG. 32 is a cross section of the pump shown in FIG. 31 along the line31--31 of FIG. 31.

FIG. 33 is a cross section in side elevation of a third embodiment of apump employing the magnetic rotor suspension and rotation apparatus ofthe present invention.

FIG. 34 is a cross section in side elevation of a fourth embodiment of apump employing the magnetic rotor suspension and rotation apparatus ofthe present invention.

FIG. 35 is a cross section in end elevation of a second preferredarrangement of stator coils in a pump employing the magnetic rotorsuspension and rotation apparatus of the present invention andparticularly adapted for use in the pumps illustrated in FIGS. 31-34.

FIG. 36 is a block diagram of portions of the rotation control system ofan apparatus, constructed in accordance with the present invention,having three stator coils to rotate a rotor.

FIG. 37 is an isometric view of two pumps employing the apparatus of thepresent invention illustrating the use of such pumps as an artificialheart.

FIG. 38 is an isometric view of a pump constructed in the manner shownin FIG. 34 illustrating the use of such pump as an assist to the naturalheart.

DESCRIPTION OF FIGURES 1-26

Referring now to the drawings in general and to FIGS. 1-3 in particular,shown therein and designated by the general reference numeral 40 is anapparatus constructed in accordance with the present invention toinclude a magnetically suspended and rotated rotor. More specifically,the apparatus 40 is a centrifugal pump particularly suited for use as ablood pump that can be implanted in the human body to replace or assistthe natural heart in the pumping of blood through the circulatory systemand, at times, the apparatus 40 will, accordingly, be referred to as thepump 40. In this particular application of the apparatus 40, the rotorthereof, indicated at 42 in FIGS. 2 and 3, is configured to act as animpellor for the pump 40 and such rotor will, accordingly, also bereferred to as the impellor 42.

The pump 40 is comprised of a housing 44 having a bore 46 formedtherethrough about an impellor support axis 48 and central portions ofthe bore 46 are enlarged to form an impellor chamber 50 in which theimpellor 42 is suspended as will be discussed below. Portions of thebore 46 to one side of the impellor chamber 50 form a first inletpassage 52 to the impellor chamber 50 and portions of the bore 46 of theother side of the impellor chamber 50 form a second inlet passage 54 tothe impellor chamber 50. An outlet passage 56 is formed in centralportions of the housing to extend tangentially from radially outermostportions of the impellor chamber 50 as shown in FIG. 3. An ever-wideninggroove 58 is formed in the housing 44 to extend circumferentially aboutthe impellor chamber 50 to provide a smooth transition from the impellorchamber 50 to the outlet passage 56 and the impellor chamber 50 isformed by smoothly flared portions of the bore 46 to provide for laminarflow of blood from the inlet passages 52, 54 to the outlet passage 56,thereby preventing stagnation of blood in the pump 40 or the formationof closed eddies without blood exchange that could lead to coagulationof blood within the pump 50. Similarly, the housing 44 is constructedof, or coated with, a plastic, or other, material that is physically andchemically compatible with blood so that, with the smooth transitionsfrom the inlet passages 52, 54 to the impellor chamber 50 and from theimpellor chamber 50 to the outlet passage 56, no injury or blooddamaging reaction will be occasioned to blood which might be pumped bythe pump 40 arising from the contact between the blood and the interiorof the housing 44.

The impellor 42 is similarly constructed of, or coated with, a rigid,blood-compatible material, e.g. plastic as shown, and is similarlyshaped to provide for smooth flow of blood across the surface of theimpellor 42. In particular, in the pump 40, the impellor 42 is rotatedabout an impellor rotation axis 60 which is maintained coincident withthe support axis 48, in a manner to be discussed below, and the impellor42 has two conical end portions, a first end portion 62 and a second endportion 64, having apices through which the rotation axis 60 extends.The bases of the portions 62 and 64, at which such portions are joined,are rounded as shown at 66 in FIG. 2 to provide for laminar flow ofblood across the surface of the impellor 42.

The impellor 42 is positioned within the impellor chamber 50 by amagnetic suspension assembly (not numerically designated in thedrawings) that is comprised of: a permanent magnet impellor supportassembly 68, the form of which has been particularly illustrated in FIG.4 (the permanent magnet impellor support assembly 68 will sometimes bereferred to herein as a permanent magnet rotor support assemblyconsistently with other practical applications of the present inventionthat has been noted above); and an electromagnet 70; and anelectromagnet control circuit 72 that has been particularly illustratedin FIG. 8.

Referring first to the permanent magnet impellor support assembly 68,such assembly is comprised of: a first housing magnet 74, having theform of a ring, that is mounted within the housing 44 to extendcircumferentially about portions of the impellor chamber 50 adjacent thefirst inlet passage 52; a second housing magnet 76, similarly having theshape of a ring, that is mounted in the housing 44 to extendcircumferentially about portions of the impellor chamber 50 adjacent thesecond inlet passage 54; a first impellor magnet 78, having the form ofa cylinder, that is mounted within the impellor 42 to extend axiallyalong the impellor rotation axis 60 near the apex of the first endportion 62 of the impellor 42; and a second impellor magnet 80,similarly having the form of a cylinder, that is mounted within theimpellor 42 to extend axially along the impellor rotation axis 60 nearthe apex of the second end portion 64 of the impellor 42. Preferably,the magnets 74-80 are constructed of a cobalt-samarium alloy to providethe magnets 74-80 with a high retentivity that will result in largepermanent magnet forces on the impellor 42 to support the impellor 42within the impellor chamber 50.

The relative positions of the magnets 74-80 and the directions in whichthe magnets 74-80 are magnetized are selected, in a manner that has beenindicated in FIG. 4, to provide a permanent magnet force profile on theimpellor 42 that has been graphically illustrated in FIGS. 5 and 6.(FIG. 4 has been drawn for the preferred case, achievable by selectionof the magnets 74-80, in which the magnets 74-80 are homogeneouslymagnetized so that their magnetic axes coincide with their geometricaxes.) In particular, and as shown in FIG. 4, the magnets 74-80 areaxially magnetized in the same direction so that magnetic polesindicated in FIG. 4 appear at the radially extending faces of thehousing magnets 74, 76 and at the ends of the impellor magnets 78, 80.The separation of the housing magnets 74, 76 is selected with respect tothe separation of the impellor magnets 78, 80 so that, when the impellor42 (schematically indicated in FIG. 4 by dashed lines connecting theimpellor magnets 78, 80 and numerically indicated by the numericalindication 42 for the impellor 42) is axially centered in the impellorchamber 50, the outside ends 82 and 84 of the impellor magnets 78 and 80respectively will be in axial alignment with the inside faces 86 and 88of the housing magnets 74 and 76 respectively. Thus, a north pole on oneof the impellor magnets 78, 80 will be surrounded by a north pole of oneof the housing magents 74, 76 and a south pole on the other of theimpellor magnets 78, 80 will be surrounded by a south pole on the otherof the housing magnets 74, 76.

With the magnets 74-76 so magnetized and positioned, axial forces thatthe permanent magnet support assembly 68 exerts on the impellor 42, viathe mounting of the impellor magnets 78, 80 thereon, will cancel whenthe impellor 42 is axially centered in the impellor chamber 50 to definea null position of the impellor 42 in the housing 44. Such position isindicated in FIG. 4 as a point 90, representing the geometric center ofthe impellor magnet 78 and 80, located at the geometric center of thehousing magnets 74 and 76 at which the geometric center of the impellormagnets 78, 80 will be located when the impellor 42 is centered in theimpellor chamber 50. (The geometric center of magnets 78, 80 is locatedat the geometric center of the impellor 42 for a reason to be discussedbelow.) Should the impellor 42 be axially shifted away from the nullposition; that is, should the geometric center of the impellor magnets78, 80 move away from the point 90 along the x axis indicated in FIG. 4,such axis coinciding with the housing support axis 48 in FIG. 2, theaxial force on the impellor 42 will have the form of the curve 92 shownin FIG. 5 which is a graph of the axial component of the permanentmagnetic force (plotted as the ordinate) versus the position of theimpellor along the housing support axis 48 (plotted as the abscissa)with the origin of the graph corresponding to location of the impellor42 at the null position. As shown in such Figure, should the center ofthe impellor 42 move from the point 90 in the direction of increasing x(to the right in FIG. 4), the axial component, F_(mx), of the permanentmagnet force on the impellor will have a positive value; that is theaxial component of the permanent magnet force on the impellor will alsobe to the right in FIG. 4. Conversely, should the impellor move to theleft of the null position indicated in FIG. 4, the axial component ofthe permanent magnet force on the impellor 42 will also be to the leftas indicated by negative values of the axial component force curve 92 inFIG. 5. Thus, the permanent magnet impellor support assembly 68 exertsno axial force on the impellor 42 at such times that the impellor 42 isin the null position in which the geometric center of the impellormagnets 78, 80 is coincident with the geometric center of the housingmagnets 74 and 76 and exerts an axial force on the impellor 42 tendingto drive the impellor 42 away from the null position at such times thatthe impellor is axially displaced from the null position so that thenull position is a position of unstable equilibrium with respect to anaxial degree of freedom of the impellor 42 in the housing 44.

However, with respect to radial movement of the impellor 42, the nullposition 90 is a position of stable equilibrium for the impellor 42 and,moreover, the position of the impellor 42 in which the rotation axis 60parallels the support axis 48 is a position of stable equilibrium forangular degrees of freedom of the impellor about any axis perpendicularto the x axis of FIG. 4. (Because of the cylindrical symmetry of thepermanent magnet impellor support assembly 68, the permanent magnets74-80 exert essentially no torque about the x axis on the impellor 42for any position of the impellor 42 in the impellor chamber 50.) Theradial and angular stability of the impellor 42 can be seen from a graphof the radial component of the permanent magnet force on one of theimpellor magnets 78-80 versus displacement of the magnet from the x axisin FIG. 4; that is, a graph of the radial force on the magnet as afunction of a coordinate r shown in FIG. 4. (Because of the cylindricalsymmetry of the magnets 74-80, the coordinate r can extend in anydirection from the x axis.) Such a graph has been included for theimpellor magnet 78 as FIG. 6 in which the radial component of thepermanent magnet force on the impellor magnet 78 has been plotted on theordinate of the graph in FIG. 6 and the radial displacement of themagnet 78 has been plotted along the abscissa. With the permanentmagnets 74-80 magnetized and relatively positioned as shown in FIG. 4,the radial component, F_(mr), of the permanent magnet force on theimpellor magnet 78 has the general form of the curve 94 in which suchcomponent is negative for all positive values of the variable r thatindicates displacement of the axis of the magnet 78 from the x axis.That is, should the magnet 78 become displaced radially from the axis x,which lies along the housing support axis, the housing magnets willexert a force on the impellor magnet 78 that tends to return theimpellor magnet 78 to the x axis. Similarly, the housing magnets willtend to maintain the axis of the impellor magnet 80 on the housingsupport axis so that any misalignment of the impellor rotation axis,along which the impellor magnets 78 and 80 extend, with the housingsupport axis, along which the x axis extends, will result in permanentmagnet forces on the impellor 42 that will tend to realign the impellorrotation axis 60 with the housing support axis 48. Because of therepulsion that exists between the magnets 74 and 78 and between themagnets 76 and 80, such repulsion arising from the juxtaposition of likemagnetic poles of the housing and impellor magnets, and the axialmagnetization of the magnets 74-80, large changes in the magnetic fieldabout the magnets 74-80 will occur for small misalignments of the axes48 and 60. Thus, the forces tending to align the axis 48 and 60 will besufficiently strong to very stably support the impellor 42 with respectto the coincidence of the axes 48 and 60.

It will thus be seen that the permanent magnet impellor support assembly68 exerts forces on the impellor 42 which tend to align the rotationaxis 60 of the impellor 42 with the housing support axis 48 whiletending to drive the impellor 42 axially away from the null position inwhich the geometric center of the impellor 42 is located at the point 90in FIG. 4 at such times that the impellor is displaced axially away fromthe null position. Moreover, in the absence of additional static axialforces on the impellor 42, only a small control force, which is suppliedby the electromagnet 70 in a manner to be discussed below, is needed tokeep the impellor at the null position as can be seen from the graph ofFIG. 5. To maintain the impellor 42 at the null position, the controlforce need only be sufficient to overcome the axial component of thepermanent magnet force on the impellor and such axial component is smallso long as the impellor 42 is near the null position as has been shownby the range 96 of the axial component of the permanent magnet force onthe impellor 42 corresponding to a small range 98 of position of theimpellor 42 about the null position in FIG. 5.

FIG. 5 has been drawn for the case in which the only axial force on theimpellor 42, other than the control force exerted thereon by theelectromagnet 70, is the force exerted on the impellor 42 by thepermanent magnet impellor support assembly 68. In this case, the nullposition 90 is also a position of mechanical equilibrium of the impellor42 and it is the fact that the position is one of mechanical equilibriumthat limits the force the electromagnet 70 must exert on the impellormagnets 78, 80 to stabilize the impellor 42 in the impellor chamber 50.The present invention contemplates the exploitation of thischaracteristic of stabilization about an equilibrium position, as wellas the general form of the axial component of the permanent magnet forceon the impellor 42, to cause the permanent magnets 74-80 to support theimpellor 42 against additional axial forces that might be exerted on theimpellor 42; for example, reaction forces on the impellor 42 which mightarise from an imbalance in the supply of blood to the two inlet passages52 and 54 of the pump housing 44. Thus, no additional energy to supportthe impellor 42 will be supplied to the electromagnet 70 to support theimpellor 42 in the impellor chamber 50 beyond the small energyrequirements necessary for stabilization of the impellor 42. The mannerin which the permanent magnets 74-80 are caused to support the impellor42 in the presence of an additional static axial force has beenillustrated in FIGS. 4 and 7.

In FIG. 4, an additional static force on the impellor 42 has beenindicated at 100 by an arrow that, for purposes of illustration, hasbeen drawn to the left in FIG. 4 so that the force 100 is in thenegative x direction in such Figure. In the presence of the force 100,the axial component of the total force, F_(TX), on the impellor,excluding the control force exerted on the impellor by the electromagnet70, as a function of impellor position has the form of the curve 102which differs from the curve 92 in FIG. 5 in that the curve 102 isshifted downwardly along the force axis from the position of the curve92 in FIG. 5. In this case, the null position for the impellor 42 (theorigin of coordinates in FIG. 7) is not a position of equilibrium forthe impellor 42; rather, the position of mechanical equilibrium for theimpellor 42 occurs for a small positive value of the axial coordinate xcorresponding to the location of the center of the impellor 42 at theposition, relative to the housing magnets 74 and 76, indicated by thedashed circle 104 in FIG. 4. Such position will be referred to herein asa control position of the rotor and, as will be discussed below, theelectromagnet control circuit 72 is constructed to pass currents throughthe electromagnet 70 to drive the impellor 42 toward the controlposition 104 at such time that the impellor 42 is displaced from thecontrol position 104. Thus, a range of positions of the impellor 42about the control position 104 at which the electromagnet 70 stabilizesthe impellor 42 corresponds to only a small range 108 in a control forcethe electromagnet 70 must exert on the impellor magnets 78, 80 tostabilize the position of the impellor 42 in the impellor chamber 50. Ascan be seen in FIG. 4, the control position is shifted from the nullposition in a direction opposite the direction in which the force 100 isexerted on the impellor 42. In the special case in which the additionalaxial force 100 is non-existent, the control position 104 is coincidentwith the null position 90.

A suitable form of construction for the electromagnet 70 has also beenillustrated in FIG. 4; that is, the electromagnet 70 is comprised of aflat, toroidal coil 110 positioned coaxially with the housing magnets74, 76 and in abutment with the inside face 86 of the magnet 74 and aflat, toroidal coil 112 similarly positioned coaxially with the magnets74, 76 and in abutment with the inside face 88 of the magnet 76 so thatthe windings of the coils 110, 112 extend circularly about portions ofthe impellor magnets 78 and 80 adjacent the ends 82 and 84 of themagnets 78 and 80 respectively. The coils 110, 112 can be connectedeither serially or in parallel and the serial connection has been shownin FIG. 4 for purposes of illustration. In such connection, theelectromagnet 70 has two input terminals 114 and 116, each providing anelectrical connection to one of the coils 110, 112, and a conductor 118connects the two coils 110, 112 together In making such connection andproviding such inputs to the coils 110, 112, it is important to observea polarity relationship between the two coils 110, 112 that has beenindicated for the serial connection by the locations of the inputterminals 114, 116 at the right hand sides of each of the two coils 110,112 in FIG. 4. Specifically, the two coils 110, 112 are connectedtogether or, in the case of parallel connection, are connected to theelectromagnet control circuit so that currents passed through the twocoils will produce a magnetic field in one direction through the centerof one coil 110, 112 and will produce a magnetic field in the oppositedirection through the center of the other coil 110, 112. With themagnetizations of the impellor magnets 78, 80 that has been shown inFIG. 4, the opposite directions of the magnetic fields produced bypassing a current through the coils 110, 112 results in the force thatone coil exerts on the impellor magnet partially disposed within suchcoil being in the same direction as the force the other coil exerts onthe other impellor magnet.

For purposes which will be discussed below, it is desirable that theimpellor 42 be light in weight and the use of two impellor magnets 78,80 in the impellor 42, rather than one impellor magnet that extendsnearly the length of the impellor 42, is utilized to limit the weight ofthe impellor 42. However, the use of two impellor magnets will alsoresult in a geometrical limitation of the force that the magnetic fieldproduced by each coil of the electromagnet 70 produces on the impellormagnet about which the coil extends, such limitation arising from thepresence of opposite magnetic poles at the two ends of each of theimpellor magnets. It has been found that a suitable construction of thecoils of the electromagnet 70 and the impellor magnets 78, 80 that willprovide efficient operation of the magnetic suspension assembly despitethis force limitation is the construction of the impellor magnets 78 and80 to have lengths approximately equal to the axial extents of themagnets 74 and 76 with the magnets 78 and 80 extending into the coils110 and 112 of the electromagnet for approximately one-third the axialextent of the coils 110 and 112 as shown in FIG. 4. (The magnet geometryhas been schematized in remaining Figures to simplify illustration ofthe present invention. The preferred geometry is that shown in FIG. 4.)The radial extents of the coils 110, 112 of the electromagnet can bevaried to adjust the relationship between the current through theelectromagnet 70 and the axial force exerted on the impellor 42 by theelectromagnet 70. Thus, the coils 110, 112 of the electromagnet 70 canbe provided with a larger outside radius than the outside radius of thehousing magnets 74 and 76 as has been shown in FIG. 2. Similarly, theinside radii of the coils 110, 112 need not be the same as the insideradii of the housing magnets 74, 76 but can be larger to accommodate theflaring of the bore 46 through the housing 44 to form the impellorchamber 50 as has also been indicated in FIG. 2.

Coming now to the electromagnet control circuit 72, shown in FIG. 8, itshould first be noted that the circuit 72 makes extensive use ofintegrated circuits to limit both the physical size of the electronicspackage of the apparatus 40 and the cost of manufacturing such package.Moreover, to insure reliability of the circuit 72, use has been made,where appropriate, of standard circuits which each carry out a specificfunction in the overall circuit 72 so that the novel aspects of theelectromagnet control circuit 72 lie in selection and combination of thespecific functional circuits of which the electromagnet control circuit72 is comprised to provide the circuit 72 with an overall, novel schemeof operation. In order to stress these novel aspects of theelectromagnet control circuit 72, individual circuits which comprise thecircuit 72 will be only briefly discussed to indicate components whichcan suitably be used in these circuits. In keeping with this stress onthe electromagnet control circuit 72 as a whole, power and groundconnections to the integrated circuits which are specified inmanufacturer's literature for the circuits have not been illustrated inthe drawings except in those instances in which it is useful to do so tobring out a feature that contributes to the operation of the circuit 72as a whole. Similarly, the power supply for the circuit 72 has not beenillustrated. It is contemplated that such power supply is a battery packthat can be recharged using a conventional recharging circuit that canbe implanted in the human body and inductively coupled to a chargingcoil positionable against the body as discussed in the aforementionedU.S. Pat. application Ser. No. 245,007. Since the requirements for thebattery pack are imposed by the requirements of standard electricalcomponents that are described in the manufacturer's literature for suchcomponents, the illustration of the battery pack and connections betweencomponents of the circuit 72 and the battery pack would serve only tocomplicate the drawings so that, in the interest of clarity ofdescription, the battery pack and connections thereto have not beenillustrated. It is to be understood that the circuit 72 has a commonground which is taken at a connection between two batteries of thebattery pack so that a variety of positive and negative voltages can besupplied to components of the circuit 72 to provide electrical power tosuch components in accordance with needs specified in manufacturer'sliterature for such components.

Referring now to FIG. 8, the electromagnet control circuit 72 comprisesan astable multivibrator 120 which has been more particularlyillustrated in FIG. 9. The multivibrator 120 is of conventionalconstruction that employs a type 555 timer 121 and a plurality ofresistors and capacitors connected thereto to provide a square wavesignal at the timer output terminal 122 which serves as the outputterminal of the multivibrator 120.

In the blood pump adaptation of the invention, a suitable frequency forthe square wave signal produced by the astable multivibrator 120 is 40kilohertz which, as will become clear below, results in a sampling timefor repositioning the impellor 42 of approximately 0.15 milliseconds.Such sampling time is short enough to provide effective control of theposition of the impellor 42 in the impellor chamber 50 and long enoughto ensure high efficiency of light emitting diodes used in theelectromagnet control circuit 72 as will be discussed below. To achievethe 40 kilohertz operating frequency, the discharge terminal 124 of thetimer is connected between fixed 1.8 kilohm and 8.2 kilohm resistors,126 and 128 respectively, the 8.2 kilohm resistor 128 is connected tothe power supply via a 2.8 kilohm variable resistor 130, the 1.8 kilohmresistor is connected via a 2.2 nanofarad capacitor to the circuitground, and the trigger and threshold terminals, 134 and 136respectively of the timer 121 are connected between the 1.8 kilohmresistor 126 and the capacitor 132. A 220 microfarad capacitor 138 isconnected between the power terminal 140 of the timer 121 and thecircuit ground to provide a short circuit for transients that mightotherwise be transmitted to other components of the electromagnetcontrol circuit 72 via the power supply as is known in the art.

The square wave signal generated by the astable multivibrator 120 isapplied to an infrared transmitter 142 that has been particularlyillustrated in FIG. 10 via a conductor 144 and to a timing circuit 146that will be discussed below via a conductor 148. Referring to FIG. 10,the infrared transmitter comprises a pnp transistor 150 which, in theblood pump application of the present invention can suitably be a typeBC 161 transistor. The emitter of the transistor 150 is connected to thepower supply via a conductor 152 and the base of the transistor 150 isconnected to the output terminal 122 of the timer 121 via the conductor144 and a resistor 154 which, in the blood pump application of theinvention, has a resistance of 5.6 kilohms. The collector of thetransistor 150 is connected to the circuit ground via a 56 ohm resistor156, a first light emitting diode 158, and a second light emitting diode160. The light emitting diodes 158 and 160 are selected to producebursts of infrared radiation when the diodes are pulsed and suitablelight emitting diodes for use in the infrared transmitter 142 are typeSFH 400 light emitting diodes.

The positioning of the diodes 158 and 160 in the pump 40 has beenillustrated in FIG. 2 to which attention is invited. A socket 162 isformed in the wall of the first inlet passage to receive the lightemitting diode 158 and the socket 162 is positioned and oriented so thatthe beam of infrared radiation produced by the light emitting diode 158is directed diametrically across the inlet passage 52 and such that thecenter of the beam is aligned with one end 164 of the impellor 42 whenthe impellor 42 is disposed in the null position thereof. Thus, the beamof infrared radiation produced by the diode 158 is partially blocked bythe impellor 42 and the degree to which such beam of radiation isblocked depends upon the position of the impellor 42 in the impellorchamber 50. Similarly, a socket 166 is formed in the wall of the secondinlet passage 54 to receive the light emitting diode 160 and the socket166 is positioned and oriented with respect to the opposite end 168 ofthe impellor 42 in the same manner that the socket 162 is positioned andoriented with respect to the end 164 of the impellor 42. Diametricallyopposed to the sockets 162 and 166, sockets 170 and 172 respectively areformed in the walls of the passages 52 and 54 to receivephototransistors 174 and 176 which are part of first and second infraredreceivers 178 and 180 respectively shown in FIG. 8.

The infrared receivers 178 and 180 are identical in construction andsuch construction has been shown for the first infrared receiver 178 inFIG. 11. In particular, the first infrared receiver 178 is comprised oftwo capacitively coupled amplifiers, one of which includes thephototransistor 174. The phototransistor 174 is preferably a type BPY61/II phototransistor having an emitter connected to the circuit groundand a collector connected to the power supply via a 5.6 kilohm resistor182. The second amplifier of the first receiver 178 is comprised of atype 2N3819 p channel field effect transistor 184 having a drainconnected to the system ground and a source connected, via a 2.7 kilohmresistor to the circuit power supply. A 100 kilohm resistor 188 providesa bias to the gate of the transistor 184 and the two amplifiers of theinfrared receiver 178 are coupled via a 10 nanofarad capacitor 190 thatis connected between the collector of the phototransistor 174 and thegate of the field effect transistor 184. The output of the firstinfrared receiver 178 is supplied on a conductor 192 connected to thesource of the field effect transistor 184 and the output of the secondinfrared receiver 180 is similarly supplied on a conductor 194 as shownin FIG. 8.

The construction of the infrared receivers 178, 180 as two capacitivelycoupled amplifiers serves to prevent ambient light from interfering withthe control of the stablization of the impellor 42. That is, ambientlight to which the pump 40 might be subjected would give rise to a DCcomponent in the output of the phototransistor 174 that would be blockedby the coupling capacitor 190 so that the signals appearing on theconductors 192 and 194 of the first and second infrared receiversrespectively are related solely to the illumination of thephototransistors 174 and 176 by the light emitting diodes 158 and 160.Use of field effect transistors in the infrared receivers serves toprovide an impedence match between the phototransistors 174, 176 and adifference amplifier 196 which receives the outputs of the infraredreceivers 178, 180 as shown in FIG. 8.

The construction of the difference amplifier 196 has been particularlyshown in FIG. 12. As illustrated therein, the difference amplifier 196comprises an operational amplifier 198 which is preferably one of fouroperational amplifiers included in a type TL084 integrated circuit Thenon-inverting input of the operational amplifier 198 is connected to theoutput of the first infrared receiver 178 via the conductor 192 and a100 kilohm resistor 200 and to the circuit ground via a 100 kilohmresistor 202. The inverting input of the operational amplifier 198 isconnected to the output of the second infrared receiver 180 via theconductor 194 and a 100 kilohm resistor 204 and is further connected tothe output of the operational amplifier 198 via a 100 kilohm resistor206. Thus, the output of the operational amplifier 198 is a signal thatis proportional to the difference in the two signals received on theconductors 192 and 194 from the two infrared receivers 178 and 180. Suchoutput, which can be positive or negative with respect to the circuitground depending upon the location of the impellor 42 with respect tothe null position thereof, is provided to an integrator 208 via avariable 100 kilohm resistor 210 and a conductor 212.

The integrator 208, which has been particularly illustrated in FIG. 13,is comprised of an operational amplifier 214, which is a second of theoperational amplifiers of the above-mentioned TL084 integrated circuit,and a 10 nanofarad capacitor 216 that is connected between the output ofthe operational amplifer 214 and the inverting input thereof so that thecapacitor 216 will store a charge in response to a signal supplied tothe inverting input of the operational amplifier 214, such charge beingproportional to the integral of the signal supplied to such inputIntegrated circuit switches 218 and 220 connect the inverting input ofthe operational amplifier 214 to the circuit ground and to the conductor212 from the difference amplifier 196 respectively so that theintegrator 208 can be periodically reset, by closing the switch 218 todischarge the capacitor 216, and subsequently connected to the output ofthe difference amplifier 196 by closing the switch 220. Subsequent tothe closure of the switch 220, a charge that is proportional to theintegral of the difference amplifier output following reset of theintegrator 208 will accumulate on the capacitor 216 in a conventionalmanner. Suitable switches for resetting the integrator 208 andsubsequently connecting the integrator 208 to the difference amplifier196 are provided by the HI-201 integrated circuit which includes foursingle pole single throw CMOS analog switches that open in response toan electrical signal and are otherwise closed. In particular, the switch220 can be opened via a signal supplied on a conducting path 222 and theswitch 218 can be opened by an electrical signal supplied on theconducting path 224 shown in FIG. 13, such paths leading to the timingcircuit 146 that has been illustrated in FIG. 15.

The output of the operational amplifier 214 of the integrator 208 isconnected, via a conductor 226, to a sample and hold circuit 228 that isconstructed as shown in FIG. 14. The sample and hold circuit 228 iscomprised of an operational amplifier 230 having a non-inverting inputconnected, via a 10 nanofarad capacitor 232, to the circuit ground and,via an integrated circuit switch 234, to the conductor 226 from theintegrator 208 The output of the operational amplifier 230 is fed backto the inverting input of the operational amplifier 230 via a conductor236 so that the output of the operational amplifier 230 will beproportional to a charge stored on the capacitor 232 The operationalamplifier 230 is conveniently another one of the four operationalamplifiers constructed on the previously mentioned 15 TL084 integratedcircuit and the switch 234 is similarly another one of the switches onthe previously mentioned HI-201 integrated circuit Like the switches 218and 220, the switch 234 is open at such times that an electrical signalis received thereby on a conductor 236 from the timing circuit 146 andis closed in the absence of such a signal.

The timing circuit 146 is constructed to count pulses produced by theastable multivibrator 120 and control the integrator 208 and sample andhold circuit 228 so that the integrator 208 periodically accumulates acharge proportional to the displacement of the impellor 42 from the nullposition thereof for a selected number of pulses produced by the astablemultivibrator 120 after which a portion of the charge is transferred tothe sample and hold circuit 228 while the integrator 208 is reset forthe accumulation of a new charge. The current through the electromagnet70 is continuously controlled, as will be discussed below, in relationto the charge stored in the sample and hold circuit 228 so that theperiodic accumulation of a charge determinative of the location of theimpellor 42 and periodic transfer of such charge to the sample and holdcircuit 228 can be used to cause the electromagnet 70 to exert forces onthe impellor 42 that will stabilize the axial position of the impellor42 in the impellor chamber 50.

The construction of the timing circuit 146 has been particularlyillustrated in FIG. 15 and FIG. 20 has been included to illustrate theoperation of the timing circuit 146, the latter of these two Figuresshowing the form of electrical signals that appear at various times andat selected points in the electromagnet control circuit 72. Referringfirst to FIG. 15, the timing circuit is comprised of a type CD4017Johnson counter 240; that is, a counter that is constructed to pass apositive voltage serially along a plurality of output terminals inresponse to a series of pulses received by the counter. Such pulses areprovided on the conductor 148 from the astable multivibrator 120, theconductor 148 being connected to the clock input terminal 242 of thecounter 240 The counter 240 can be reset by a positive voltage suppliedto a reset terminal 244 and the reset terminal 244 is connected to anoutput terminal 246 of the counter 240 that is the seventh of the outputterminals to become positive in response to a series of pulses suppliedto the clock terminal 242 of the counter 240 following reset of thecounter 240. Thus, in response to a continuous stream of pulses receivedat the clock terminal 242 of the counter 240, a repeating operation ofthe counter 240 will occur in which a positive voltage is sequentiallypassed along six output terminals of the counter 240. The first four ofthese output terminals, indicated at 248-254 in FIG. 15 are connected tothe input terminals 256-262 of a type 4002 NOR gate 264 and the outputterminal 266 of the NOR gate 264 is connected to the conductor 222leading to the switch 220 in the integrator 208. (The type 4002 NOR gateis an integrated circuit upon which two NOR gates are constructed. Onlyone of these NOR gates in the integrated circuit is used in theoperation of the timing circuit so that it is useful to refer to suchintegrated circuit as the NOR gate).

The fifth and sixth output terminals of the counter 240 to becomepositive in response to a series of pulses received by the counter 240at the clock terminal 242 following reset, the fifth output terminalbeing indicated at 268 in FIG. 15 and the sixth output terminal beingindicated at 270 in FIG. 15, are connected to two inverters of a typeCD4069 hex inverter integrated circuit 272 at input terminals 274 and276 of the circuit 272 and output terminals 278 and 280 of the circuit272, corresponding to the input terminals 274 and 276, respectively areconnected to the conductors 224 and 238 that extend, respectively, tothe switches 218 in the integrator 208 and 234 in the sample and holdcircuit 228.

Referring now to FIG. 20, shown therein is a graph illustratingelectrical signals at selected points in the electromagnet controlcircuit 72 following reset of the counter 240. For each of the curvesshown in the graph, signal strength (voltage) is plotted along theordinate and time, common to all the curves, is plotted along theabscissa. The uppermost curve 282 is the voltage at the output of theastable multivibrator 120 so that the uppermost curve 282 illustrates aseries of pulses that are simultaneously supplied to the clock terminal242 of the counter 240 and to the infrared transmitter 142. For each ofthese pulses, a positive voltage will be shifted along the line ofoutput terminals of the counter 240 and, since the graph has been drawnto illustrate signals immediately following reset of the counter 240,the first output terminal 248 of the counter 240 becomes positive withthe rise of the first pulse 289 of the curve 282. Thus, a positivevoltage will be supplied to the input terminal 245 of the NOR gate 264during the duration of the first pulse 289 of the curve 282 and up tothe rise of the second pulse of the curve 282. In response, the outputterminal 266 of the NOR gate 264 will be substantially grounded asillustrated in the second curve at 284 in FIG. 20. On the other hand,the fifth and sixth output terminals, 268 and 270 respectively, of thecounter 240 will be substantially grounded during the first pulse sothat the inputs 274 and 276 of the circuit 272 will be substantiallygrounded Thus, positive voltages appear at the inverter outputs 278 and280 during the first pulse 289 as illustrated by the curves 286 and 288respectively in FIG. 20.

Since the inverter output terminals 278 and 280 of the circuit 272 areconnected to the switches 218 and 234 in the integrator and sample andhold circuit respectively and since the switches 218 and 234 open inresponse to positive voltages supplied thereto, the switches 218 and 234will be open during the first pulse supplied to the counter 240 by theastable multivibrator 120. Similarly, since the output terminal 266 ofthe NOR gate 264 is substantially at ground voltage and is connected tothe switch 220 of the integrator 208, the switch 220 of the integrator208 will be closed during the first pulse provided by the astablemultivibrator. Such conditions of the switches 218, 220 and 234 willcontinue until the rise of the fifth pulse 291 provided by the astablemultivibrator 120 because of the connection of the first four outputterminals of the counter 240 to the NOR gate 264 which controls theswitch 220 and because of the control of the switches 218 and 234 viathe fifth and sixth output terminals of the counter 240. With the riseof the fifth pulse 291 produced by the astable multivibrator 120, thevoltage at the fourth output terminal 254 of the counter 240 drops tozero so that all four input terminals 256-262 of the NOR gate 264 becomesubstantially grounded to produce a positive voltage at the outputterminal 266 of NOR gate 264. This voltage rise is transmitted to theswitch 220 of the integrator 208, as indicated at 293 in FIG. 20, toopen the switch 220. Concurrently with the drop in voltage at the fourthoutput terminal of the counter 240 with the rise of the fifth pulseproduced by the astable multivibrator 120, a positive voltage appears atthe fifth output terminal 268 of the counter 240 and is transmitted tothe input terminal 274 of the invertor 272 to cause the output terminal280 of the invertor 272 to become substantially grounded, as shown at295 for the curve 288, so that the switch 234 in the sample and holdcircuit 228, such switch being connected to the inverter output terminal280 of the circuit 272, is closed. Thus, with the rise of the fifthpulse 291 provided by the astable multivibrator 120, the integrator 208is isolated from the difference amplifier 196 and a portion of anycharge that might have accumulated in the integrator 208 is transferredto the sample and hold circuit 228.

With the rise of the sixth pulse 297 produced by the astablemultivibrator 120, the voltage at the fifth output terminal 268 of thecounter 240 drops so that the inverter input terminal 276 of the circuit272 is substantially grounded and a positive voltage appears at theinverter output terminal 280 of the circuit 272, as shown at 299 for thecurve 288, and is transmitted to the switch 238 of the sample and holdcircuit 228 to open the electrical connection between the integrator 208and the sample and hold circuit 228 Concurrently, a positive voltageappears at the sixth output terminal of the counter 240 and istransmitted to the inverter input terminal 274 of the circuit 272 tocause the inverter output terminal 278 of the circuit 272 to becomesubstantially grounded as shown at 301 in the curve 286 in FIG. 20.Since the switch 218 of the integrator 208 is connected to the inverteroutput terminal 278 of the circuit 272, the switch 218 closes todischarge the capacitor 216 of the integrator 208 during the sixth pulseprovided by the astable multivibrator 120.

With the rise of the seventh pulse 303 provided by the astablemultivibrator, the counter 240 is reset so that the sixth outputterminal 270 of the counter 240 become grounded, causing a rise 305 inthe voltage supplied to the switch 218, thereby opening the switch 218of the integrator 208 and a positive voltage appears at the first outputterminal 248 of the counter 240 to again disable the NOR gate 264, asillustrated at 307, and close the switch 220 of the integrator 208. Theseventh pulse 303 is thus equivalent to the first pulse 289 so that thepattern of voltages appearing at the switches 220, 218 and 234 of theintegrator 208 and sample and hold circuit 228 repeats for every sixpulses delivered by the astable multivibrator 120 and such pattern is asfollows For the first four pulses of each series of six pulses deliveredby the astable multivibrator, the switch 220 of the integrator 208 isclosed and the switch 218 of the integrator 208 is open so that theintegrator can accumulate a charge porportional to the integral of asignal at the output of the difference amplifier 196 beginning with therise of the first pulse of each series of six pulses generated by theastable multivibrator 120. With the rise of the fifth pulse of eachseries of six pulses, the switch 220 of the integrator 208 opens and theswitch 234 of the sample and hold circuit 228 closes so that the chargeaccumulated in the integrator 208 is partially transferred to the sampleand hold circuit 228. With the rise of the sixth pulse, the switch 234of the sample and hold circuit 228 opens and the switch 218 of theintegrator 208 closes so that the sample and hold circuit 228 isisolated from the integrator 208 and the capacitor 216 of the integrator208 is discharged for the accumulation of a new charge in the integratorduring the next succeeding four pulses generated by the astablemultivibrator. Such accumulation begins with the first of the nextseries of six pulses delivered by the multivibrator 120, the rise ofsuch first pulse of the next series causing the switch 218 in theintegrator 208 to open and the switch 220 to close to reconnect theintegrator 208 to the difference amplifier 196.

Also shown in FIG. 20 are curves illustrating the charge accumulated inthe integrator 208 and the charge stored in the sample and hold circuit228 during a time period corresponding to eleven pulses produced by theastable multivibrator 120 beginning with the reset of the counter 240that occurs with the rise of the first of the series of pulses shown inthe curve 282. The curve 290 of FIG. 20 is a graphical depiction of thecharge accumulated in the integrator 208 and curve 292 is a graphicaldepiction of the charge stored in the sample and hold circuit 228. Ithas been assumed in drawing curve 292 that the impellor has been at thenull position thereof for a period of time prior to the first pulse 289so that no charge is stored in the sample and hold circuit 228 when thefirst pulse 289 occurs.

Concurrently with the generation of each pulse by the astablemultivibrator 120, a pulse of infrared radiation is emitted by each ofthe light emitting diodes 158 and 160 and such radiation pulses aredirected across the inlet passages 52 and 54 to impinge upon thephototransistors 174 and 176 of the infrared receivers 178 and 180. If,prior to the first of the pulses shown in FIG. 20, the impellor 42 hasbeen located at the null position thereof, the phototransistors 174 and176 will have been equally illuminated so that equal electrical signalswill have been continuously impressed on the inverting and non-invertinginputs of the operational amplifier 198 of the difference amplifier 196with the result that no signal will have appeared on the conductor 212from the output of the difference amplifier 198 for any of the pulsesthat have been generated by the astable multivibrator 120 immediatelyprior to the pulses illustrated in FIG. 20. Accordingly, as the firstpulse of the curve 282 rises, no charge will have been previouslyaccumulated by the integrator 208 and no charge will have been stored inthe sample and hold circuit 228. Assuming that the impellor 42 becomesdisplaced from the null position immediately prior to the rise of thefirst pulse of the curve 282, emission of a pulse of infrared radiationduring the first such pulse of the curve 282 will result in unequalillumination of the phototransistors 174 and 176. As a result, duringthe first pulse 289, the difference amplifier 196 will receive unequalsignals from the two infrared receivers 178, 180 so that the differenceamplifier 196 will provide a non-zero signal on the conductor 212 thatprovides an input to the integrator 208. The integral of this signal isaccumulated in the integrator 208 as indicated by the portion 294 of thecurve 290 in FIG. 20. During the interim between the first and secondpulses of curve 282 in FIG. 20, no power is supplied to the lightemitting diodes 158 and 160 so that the phototransistors of the infraredreceivers 178 and 180 are not illuminated. Thus, during the interimbetween these first two pulses, and between any other pair of pulses,both inputs of the difference amplifier 192 are effectively grounded sothat no accumulation of charge occurs in the integrator 208 betweenpulses produced by the astable multivibrator 120 as indicated by theflat portions 296-302 of the curve 290 in FIG. 20. During the second,third and fourth of the first six pulses of the series shown in thecurve 282, the light emitting diodes 158, 160 will again provide pulsesof infrared radiation directed across the pump input passages 52 and 54and, assuming the impellor 42 remains displaced from the null positionin the same direction as the displacement of the impellor 42 from thenull position during the first pulse 289, the phototransistors of theinfrared receivers 178 and 180 will remain unequally illuminated so thatthe difference amplifier 196 will again receive unequal signals from theinfrared receivers to provide a signal, having the same polarity as thesignal provided during the first pulse 289 to the integrator 208. As theresult, additional accumulations of charge in the integrator 208 willoccur for the second, third and fourth pulses shown in the curve 282 ofFIG. 20 as indicated by the sloped portions 304-308 of the curve 290.With the rise of the fifth pulse of the series shown in the curve 282, aportion of the charge accumulated in the integrator 208 will betransferred to the sample and hold circuit via the above describedopening of the switch 220 and closure of the switch 234 so that a chargewill appear on the capacitor 232 of the sample and hold circuit 228 asindicated by the portion 310 of the curve 292. Such charge will remainon the capacitor 232 until the switch 234 of the sample and hold circuit228 is again closed. That is, such charge will remain on the capacitor234 for a series of six pulses delivered by the astable multivibratorbeginning with the rise of the fourth pulse of each series of six pulsesutilized in the control of the switches of the integrator 208 and sampleand hold circuit 228. With the rise of the last pulse of the first sixmember series shown in the curve 282, the switch 218 is closed to resetthe integrator as indicated by the drop 312 of the curve 290. With therise of the seventh pulse 303, such pulse being the first of a newseries of six pulses, a new charge is accumulated in the same stepwisefashion in the integrator 208 for the next four pulses produced by theastable multivibrator 120 as has been indicated by the zig zag portion314 of the curve 290 in FIG. 20. (The portion 314 of the curve 290 hasbeen drawn with an amplitude that is reduced with respect to the portionof the curve 290 produced by the first four pulses shown at 282 toreflect the effect of the onset of impellor repositioning that occurswhen a charge is transferred into the sample and hold circuit with thepulse 291.) With the rise of the fifth pulse of the second series of sixpulses, indicated at 315 for curve 282 in FIG. 20, the charge that isaccumulated during the first four pulses of the second series of sixpulses is transferred to the sample and hold circuit 228 as indicated bythe portion 316 of the curve 292 and such charge remains stored in thesample and hold circuit for six of the pulses produced by the astablemultivibrator 120 beginning with the rise of the fifth pulse of eachseries of six pulses generated by the multivibrator 120. Thus, for thefirst four of each series of six pulses produced by the astablemultivibrator, a charge is accumulated in the integrator 208 and istransferred to the sample and hold circuit beginning with the fifthpulse of the series. With the rise of the sixth pulse, the integrator isreset and a new accumulation begins with the rise of the first pulse ofthe next series of six pulses. The sample and hold circuit receives aportion of each accumulation with the rise of the fifth pulse of theseries and stores such portion for six pulses so that the charge storedin the sample and hold circuit 228 reflects the average displacement ofthe impellor 42 during a time period corresponding to six pulsesproduced by the astable multivibrator just prior to the transferal ofcharge from the integrator 208 to the sample and hold circuit 228. Thus,the magnetic control circuit 72 develops a signal which is indicative ofthe location of the impellor 42 during a time period corresponding tosix pulses of the astable multivibrator and such signal is used tocorrect the location of the impellor during an equal time interval inwhich a new correction signal is generated. Such correction is effectedby first and second controllers, 318 and 320 respectively and a poweramplifier 322 as will now be discussed.

The sample and hold circuit 228 provides a signal at the output of theoperational amplifier 230 the circuit 228 includes that is proportionalto the charge on the capacitor 232 and such signal is transmitted to thefirst controller 318 via a conductor 324. The first controller 318,which has been particularly illustrated in FIG. 16, is an amplifier thatincludes an operational amplifier 326 and a feedback network made up ofa 2.2 nanofarad capacitor 328 and a 100 kilohm resistor 330 connected inparallel between the output terminal of the operational amplifier 326and the inverting input terminal thereof.

The signal from the sample and hold circuit 228 is transmitted via a69.8 kilohm resistor 332 and 47 nanofarad capacitor 334 to the invertinginput terminal of the operational amplifer 326 and a summing network,comprised of two 210 kilohm resistors 336, 338 and one 150 kilohmresistor 340, is connected to the non-inverting input of the operationalamplifier 326 at a junction between the three resistors 336-340. Theopposite end of the resistor 340 is grounded so that the signal suppliedto the non-inverting input terminal of the operational amplifier 326 isthe sum of two signals introduced via the two resistors 336 and 338. Thesignal supplied via the resistor 336 is derived from a zero-adjustpotentiometer 342, the resistor 336 being connected to the wiper arm ofthe potentiometer 342. The potentiomenter 342 can suitably be a 10kilohm resistor and the ends of the potentiometer 342 can suitably beconnected to the power supply so that a 15 volt signal is supplied toone end of the potentiometer 342 and a signal of -15 volts is suppliedto the other end thereof. The second signal supplied to thenon-inverting input of the operational amplifier 326 is derived from thesecond controller 320 via a conducting path 344 shown in FIGS. 8, 16 and17.

The operational amplifier 326 is suitably one of four operationalamplifiers of a type TL084 integrated circuit and two of remainingoperational amplifiers of such integrated circuit are used in the secondcontroller 320 as shown in FIG. 17. In particular, the second controller320 is comprised of a low pass filter that, in turn, is comprised of oneof the remaining operational amplifiers of the TL084 integrated circuit,indicated at 346 in FIG. 17, a capacitor 348 and resistors 354 and 355,357. The non-inverting input of the operational amplifier 346 isconnected to the circuit ground and the inverting input of theoperational amplifier 346 is connected via resistors 354 and 355,connected in series, to the output of the first controller 318 viaconductor identified by the numeral 352 in FIGS. 16 and 17. Thecapacitor 348 is connected between the circuit ground and the junctureof the resistors 354 and 355 to filter high frequency components of thesignal present in the output of the first controller 318 and theresistor 357 is connected between the inverting and output terminals ofthe operational amplifier 346 as a feedback resistor as is conventional.

The output signal from the filter that includes the operationalamplifier 346 is provided to one end of a 0-250 kilohm potentiometer360, the other end of which is grounded, and a portion of this signal isprovided to the inverting input of an operational amplifier 356 via aresistor 368. Feedback for the operational amplifier 356 is provided bya 100 nanofarad capacitor 362 and a 10 kilohm resistor 364 that areconnected between the output terminal of the operational amplifier 356and the non-inverting input terminal thereof. The non-inverting input ofthe operational amplifier 356 is connected to the wiper arm of a 500kilohm input current compensation potentiometer 366, one end of thepotentiometer 366 being grounded. Conductor 344, to which the resistor338 shown in FIG. 16 is connected, is also connected to the outputterminal of the operational amplifier 356 of the second controller 320so that one of the two signals that are supplied to the non-invertinginput terminal of the operational amplifier 326 of the first controller318 is provided by the second controller 320 operating in response tothe output signal of the first controller 318.

The function of the second controller 320 is to minimize the consumptionof energy by the impellor suspension system by effecting the abovementioned limitation on the use of the electromagnet 70 to stabilizationof the support of the impellor 42 by the permanent magnet impellorsupport assembly 68. As has been noted, the permanent magnets of theassembly 68 can be used to support the impellor 42 against a staticaxial force by shifting the position at which the impellor 42 issupported in the housing 44 from the null position, defined as anequilibrium position for the impellor under only those forces exertedthereon by the permanent magnet impellor support assembly 68, to acontrol position which is an equilibrium position for the impellor underthe permanent magnet forces and an additional axial force that might beexerted on the impellor 42. Should such an additional axial force beexerted on the impellor 42 while the position of the impellor 42 isstabilized at the null position, the signals provided to the differenceamplifier 196 by the infrared receivers 178, 180 would include a directcurrent component, such component arising from a persistent small shiftin the position of the impellor 42 in the direction of the static axialforce as opposed to random variations in position of the impellor 42about the null position Such direct current component would beintegrated and stored in the sample and hold circuit 228 so that anoutput signal from the first controller 318 would also contain a directcurrent component. Such component is transmitted to the operationalamplifier 356 of the second controller 320 by transmitting the outputsignal from the first controller 318 to the filter circuit of the secondcontroller 320 constructed on the operational amplifier 346 andconnecting the output of such filter circuit to the operationalamplifier 356. The operational amplifier 356 then injects a signal intothe non-inverting input terminal of the operational amplifier 326 of thefirst controller 318 to temporarily increase the current at the outputterminal of the operational amplifier 326 of the first controller 318.Elimination of the direct current component occurs by providing acurrent to the electromagnet 70 that will shift the impellor 42 to thecontrol position in which the permanent magnet impellor support assembly68 will exert a force on the impellor 42 that balances permanentmagnetic and all other long term axial forces thereon.

The establishment of the control position for the impellor 42 that isdisplaced from the null position thereof, or from a previouslyestablished control position, entails an initial increase in the currentthat is supplied to the electromagnet 70 to move the impellor 42 againsta static axial force exerted thereon so that the energy saving providedby the second controller 320 occurs only when the static axial forcepersists for a length of time sufficient for the initial additionalexpenditure of energy to be exceeded by the additional energy that wouldhave to be supplied to the electromagnet 70 to maintain the impellor 42at the null position or a previously established control position in thepresence of the static axial force. To insure that the second controller320 will react only to long term axial forces that persist long enoughto outweigh the energy required to establish a new control position forthe impellor 42, the time constant for the capacitor 348 and resistor354 of the second controller 320 is selected, in the adaptation of theinvention to the blood pump application, to be approximately one to twoseconds. Such time constant can conveniently be achieved by selectingthe capacitor 348 and the resistor 354 to have values of one or twomicrofarads and one megohm respectively.

The power amplifier 322, which has been particularly illustrated in FIG.18, receives the output of the first controller 318 via a conductor 370that is connected to the output terminal of the operational amplifier326 and provides a control current to the electromagnet 70. The poweramplifier 322 is constructed to drive the electromagnet 70 in accordancewith the current, rather than the voltage, needed to reposition theimpellor 42 should the impellor 42 become displaced from the controlposition so that the electromagnet control circuit 72 responds rapidlyto shifts in position of the impellor despite the inductive load; thatis, the electromagnet 70, driven by the electromagnet control circuit72. To this end, the power amplifier 322 is comprised of two stages: apower stage indicated in dashed lines at 372 in FIG. 18 and a controlstage (not numerically designated in the drawings) that drives the powerstage in a manner that will result in current, rather than voltage,control of the power amplifier 322.

Referring first to the power stage 372, such stage is a conventionalpush-pull amplifier comprised of an npn power transistor 374 (preferablya type MJ3001) and a pnp power transistor 376 (preferably a type MJ2501)having emitters connected together via two 0.27 ohm resistors 378 and380. The collectors of the transistors 374 and 376 are connected topositive and negative supply terminals, 382 and 384 respectively, andthe output of the power stage 372 at the junction of the two resistors378 and 380 is connected via a conductor 386 to the input terminal 114of electromagnet 70. The input terminal 116 of the electromagnet 70 isconnected via a 0.47 ohm resistor 388 to the circuit ground. The inputto the power stage is at a conductor 390 that is connected to the basesof the transistors 374 and 376 via 2.2 kilohm resistors 392 and 394. Thebases of the transistors 374 and 376 are also connected to the circuitground via 33 nanofarad capacitors 396 and 398 and to the outputprovided by the conductor 386 via a plurality of diodes 400 for thetransistor 374 and a plurality of diodes 402 for the transistor 376. A10 nanofarad capacitor 404 is connected between the conductors 386 and390 that provide the output and input respectively for the power stage374 and 100 microfarad capacitors 406 and 408 are connected between thecollectors of the transistors 374 and 376 respectively and the circuitground to prevent a signal from the power stage output from beingintroduced into the control stage of the power amplifier 322.

The control stage of the power amplifier 322 is comprised of anoperational amplifier 410 having an output terminal that is connected tothe conductor 390 forming an input to the power stage 372 and aninverting input terminal that is connected to a voltage divider,comprised of serially connected 100 kilohm and 10 kilohm resistors 412and 414 that are connected in parallel across the 0.47 ohm resistor 388so that a portion of the voltage across the resistor 388 is injectedinto the inverting input terminal of the operational amplifier 410. Thenon-inverting input terminal of the operational amplifier 410 isconnected to the wiper arm of a 100 kilohm potentiometer 416, one end ofwhich is connected to the circuit ground and the other end of which isconnected to the conductor 370 leading to the output terminal of theoperational amplifier 326 of the first controller 318.

The above-described construction of the power amplifier 322 results inthe power amplifier 322 having characteristics which have beenillustrated in FIG. 19 in which signal strengths at several places inthe circuit 72 have been plotted versus time. In the upper of the threegraphs of such Figure, a typical output for the first controller 318 hasbeen plotted as the curve 418 which illustrates the voltage at theoutput terminal of the operational amplifier 326 (the ordinate of theupper graph) as a function of time, time being plotted along theabscissa, for an assumed step output. For effective control of theposition of the impellor 42, it is desired that the force theelectromagnet 70 exerts on the permanent magnets 78 and 80 mounted onthe impellor 42 follow the curve 418 so that, since the magnetic fieldproduced by the electromagnet 70 is proportional to the currenttherethrough, it is desirable that the current through the electromagnet70 closely approximate the curve 418 shown in FIG. 19. Such current isshown by the curve 420 in FIG. 19 in the lowermost graph of such Figure,the current through the electromagnet 70 being plotted as the ordinatein the lowermost graph in FIG. 19 as a function of time along theabscissa. (For purposes of comparison, the current that would result fora constant voltage applied to the electromagnet 70 has been shown indashed lines at 421 in FIG. 19.) To achieve this correspondence betweenthe current through the electromagnet 70 and the voltage at the outputterminal of the operational amplifier 326 of the first controller 318,the voltage at the output terminal of the operational amplifier 410 ofthe control stage of the power amplifier 322 is made proportional to thedifference between the voltage across the resistor 388 of the poweramplifier 322 and the voltage supplied to the power amplifier 322 by thefirst controller 318. Thus, should the first controller 318 deliver asignal such as has been illustrated by the curve 418 in FIG. 19 to thepower amplifier 322; that is, a signal having a step preceeded by a nullsignal, the input to the operational amplifier 410 of the poweramplifier 322 will, initially, be large corresponding to the absence ofa voltage across a resistor 388 by means of which the electromagnet 70is grounded. Thus, the voltage at the output of the operationalamplifier 410 of the power amplifier 322 will initially be a largevalue, as indicated by the curve 422 in FIG. 19, to overcome inductiveeffects that tend to delay the establishment of a current through theelectromagnet 70. Such voltage then decreases in response to theestablishment of the current through the electromagnet 70 so that,should the initial signal indicated by the curve 418 persist, thevoltage at the output terminal of the operational amplifier 410 willeventually attain a steady state value as indicated by the center graphof FIG. 19. By causing the voltage at the input of the power stage 372of power amplifier 322 to be large at such times that the currentthrough the electromagnet 70 is small, the current through theelectromagnet 70 is caused to substantially follow the signal that thefirst controller 318 provides to the power amplifier 322 resulting in arapid response time for the power amplifier 322 that prevents theimpellor from making wide excursions from the control position that willrequire large amounts of energy to correct. Thus, the current, asopposed to voltage, control that is built into the power amplifier 322additionally contributes to a low power consumption for the suspensionsystem of the present invention.

In addition to the above-described magnetic suspension assembly, theapparatus 40 comprises a rotor (impellor in the case of a pump) driveassembly (not numerically designated in the drawings) that spins therotor (impellor in the case of a pump) 42 about the rotor (impellor inthe case of a pump) axis 60. One preferred form of the rotor driveassembly, particularly useful in the case in which the apparatus 40 is apump having the form shown in FIG. 1, has been illustrated in FIGS.21-26.

Referring first to FIG. 21, and with additional reference to FIG. 2, theimpellor drive assembly is comprised of a shorting ring 424 that isdisposed within the impellor 42 to extend in a circle about the impelloraxis 60 as shown in FIG. 2. As can also be seen in FIG. 2, the shortingring 424 is positioned axially midway between the ends 164, 168 of theimpellor 42 so that the portions of both the magnetic suspensionassembly and the impellor drive assembly that are mounted on theimpellor 42 are symmetrically positioned thereon. That is, theseportions of the two assemblies exhibit cylindrical symmetry about theimpellor axis 60 and bilateral symmetry about a plane perpendicular tothe axis 60 midway between the ends of the impellor 42. This symmetry ofportions of the magnetic suspension and rotor drive assemblies mountedon the impellor 42 is utilized to provide a further minimization in thepower requirements of the apparatus 40 as will now be described.

As shown in FIG. 2, a cavity 426 is formed in central portions of theimpellor 42 and such cavity has the same symmetry characteristics as theshorting ring 424 and the magnets 78 and 80 mounted on the impellor 42.Thus, since the two end portions 62 and 64 of the impellor 42 areidentical, to again have the same symmetry characteristics, the combinedcenter of gravity of the impellor 42 and portions of the drive andsuspension assemblies thereon is located at the geometric center of theimpellor 42; that is, at the point indicated at 428 in FIG. 2.Similarly, because of the symmetry of the impellor 42, the center ofbuoyancy of the impellor 42 is also located at the point 428 with thenet result that the gravitational force and buoyant force on theimpellor 42 cannot produce a couple on the impellor 42. Rather, at most,these two forces can produce only a resultant force that extends alongthe vertical The size of the cavity 426 in the impellor 42 is selectedto adjust the average specific gravity of the impellor 42 and portionsof the magnetic suspension and rotor drive assemblies on the impellor42; that is, a specific gravity determined by dividing the weight of theimpellor and portions of the magnetic suspension and drive assembliesmounted thereon by the volume of the impellor 42, to match the specificgravity of a liquid which is pumped by the pump 40. In the case in whichthe pump 40 is used as a blood pump, such average specific gravity isapproximately 1.056 to match the specific gravity of blood The matchingof the average specific gravity of the impellor and portions of themagnetic suspension and impellor drive systems mounted thereon, achievedin part by using two permanent magnets 78 and 80 in the impellor 42 aspart of the magnet suspension assembly, and the positioning of thecenter of gravity of the impellor 42 and portions of these twoassemblies mounted thereon at the center of buoyancy of the impellor 42has the result that the impellor 42 reacts to accelerations of the pump40 in precisely the same manner that an equal volume of blood having thesame position as the impellor 42 would react to an acceleration of thepump 40. Thus, should the pump 40 be implanted in a person, noadditional energy expenditure by the magnetic suspension assembly wouldbe required to accelerate the rotor 42 should the person move to giverise to an acceleration of the pump housing 44. Rather, the work thatwould have to be done on the impellor 42 to cause the impellor 42 tomove with the housing 44 would be supplied by the internal walls of thehousing 44 in the same manner that such work is supplied by the internalwalls of the housing 44 to cause blood within the housing 44 to beaccelerated with the housing 44. Thus, again, the energy required to beexpended by the magnetic suspension assembly is only that energyrequired to stabilize the support of the impellor 42 by the permanentmagnet impellor support assembly 68. Since, as has been noted, suchstabilization is accomplished by maintaining the impellor 42substantially at an equilibrium position, very little energy is requiredto stably support the impellor 42 within the impellor chamber 50.

As shown in FIGS. 2 and 21, the impellor (rotor) drive assembly for thepump 40 further comprises a stator (not numerically designated in thedrawings) that includes two ferromagnetic pole pieces 430 and 432positioned to opposite sides of the shorting ring 424. Each of the polepieces 430, 432 comprises a ring portion 434 disposed coaxially with theshorting ring 424 and a plurality of projections 436 that extend fromthe ring portion 434 toward the shorting ring 424. In one preferredembodiment of the invention, each pole piece is provided with twelveprojections 436, equally spaced about the ring portion 434, and the polepieces 430, 432 are positioned to axially align the projections 436 ofthe pole piece 432 with the projections of the pole piece 430. Twocoils, 438 and 440, are wrapped on the projections 436 as shown in FIG.21; that is, the coil 438 is serially wrapped about every other set offacing projections with the senses of the windings of the coil 438 fromone set of projections 436 to the next being selected such that themagnetic field reverses in direction from one set of projections wrappedwith the coil 438 to the next set of such projections 436. The coil 440is similarly wrapped on the remaining projections 436 of the pole pieces430, 432 so that the shorting ring 424 can be magnetically rotated, torotate the impellor 42, by supplying alternating currents having thesame frequency and amplitude, but phase shifted by 90° , to the coils438 and 440.

In addition to the stator formed by the pole pieces 430 and 432 and thecoils 438 and 440, the impellor drive assembly for the apparatus 40comprises a rotor control circuit 458 which has been illustrated inblock form in FIG. 22. In such Figure and in FIG. 21, the coils 438 and440 have been indicated as having terminals 450 and 452 (for the coil438) and 454 and 456 (for the coil 440) to indicate the manner in whichthe coils 438 and 440 are connected to the rotor control circuit 458. Ascan be seen in these Figures, the terminals 452 and 456 of the coils 438and 440 respectively are connected to the circuit ground so thatrotation of the impellor 42 can be effected by providing phase shifted,alternating current signals to the terminals 450 and 454.

It is contemplated in the present invention that the rotation rate ofthe rotor 42; that is, the impellor 42 in the pump adaptation of theinvention, is to be controlled in accordance with a preselectedrelationship between such rotation rate and the value of a measurablephysical quantity. In particular, where the invention is adapted for useas a blood pump, the rotation rate of the impellor 42 can be controlledto cause the pump to mimic the physiological pumping characteristics ofthe natural heart. Such characteristics are embodied in the so-calledFrank-Starling effect which relates the pumping rate of each half of thenatural heart and the change in pressure across each half of the heartto pressure at the inlet of each half of the heart. The effect thuslumps the interaction between each half of the heart and the remainderof the body into a single parameter, inlet pressure, that can bemeasured so that the interaction between the heart and the body can beduplicated in an artificial heart or a heart assist device bycontrolling the flow of blood through a pump that replaces or assiststhe heart to mimic this effect.

To this end, and as shown in FIG. 2, a socket 464 is formed in the wallof the first inlet passage 52 to receive a pressure sensor 466, asuitable sensor being one of the model 1800 series pressure transducersmanufactured by Foxboro/ICT of San Jose, California, such transducerbeing selected to cover a range of pressure consistent with theparticular application to which a pump that includes the rotorsuspension and rotation system of the present invention is adapted.These transducers are analog devices and the rotor control circuitfurther comprises a conventional A/D convertor 468 to which the sensor466 is connected, via conductor 467, so that each pressure sensed by thesensor 466 is expressed as an eight bit binary number at eight outputterminals of the convertor 468. Both the frequency and amplitude of thealternating current signals supplied to the coils 438 and 440 arecontrolled in the present invention in accordance with the eight bitbinary number that appears at the output terminals of the A/D convertor468.

To establish appropriate values for the frequency and amplitude of thesignals transmitted to the coils 438 and 440, the eight bit number atthe output terminals of the A/D convertor 468 is transmitted, via a busindicated by a broad arrow 470 in FIGS. 22 and 23, to the inputterminals of an encoder 472 that has been shown in more detail in FIG.23. (The rotor control circuit 458 is a hybrid analog-digital circuit.In order to clearly bring out the operation of this circuit, theconvention has been adopted in the drawings of illustrating buses whichtransmit digitally expressed signals as broad arrows and conductorswhich transmit analog signals as lines.) As shown in FIG. 23, theencoder 472 is comprised of a first memory device 474 which ispreferably a type MM2716 PROM, the bus 470 being connected to theaddress terminals of the device 474. (For clarity of disclosure,integrated circuits used in the control circuit 458 that have beenselected to provide specific functions have been identified bymanufacturer's type number in FIGS. 23-25. The identified integratedcircuits, and their interconnections, provide a preferred embodiment ofthe control circuit 458 but it will be recognized that substitutions canbe made for the integrated circuits so identified.) The device 474 isprogrammed, in a manner to be discussed below, so that the digitalnumber appearing at the data terminals of the device 474 for eachpressure-determined digital number that appears at the address terminalsthereof will cause an oscillator 476, constructed as shown in FIG. 24,to produce an alternating signal having a frequency that is appropriateto the digitally expressed pressure at the input terminals of theencoder to cause the pump 40 to mimic the natural heart. Additionally,the encoder 472 comprises a second memory device 478, also preferably atype MM1702A PROM, that also receives the eight bit digital signalpresent at the data terminals of the memory device 474, such signalbeing supplied to the address terminals of the memory device 478 via abus 480. In response to each digitally expressed signal received at theaddress terminals of the memory device 478, the memory device 478produces a digitally expressed signal at the data terminals thereof andsuch digitally expressed signal is used to fix the amplitude of thesignal supplied to the coils 438 and 440 in a manner that will bediscussed below. In order to utilize the digitally expressed signalsdeveloped in the memory devices 474 and 478, the encoder furthercomprises D/A converters 475 and 479 which receive the outputs of thedevices 474 and 478 respectively and output corresponding analog signalson conductors 525 and 549 respectively.

Referring now to FIG. 24, the oscillator 476 is comprised of a typeXR2209 oscillator/timer 481 having resistors and capacitors connected toterminals thereof in a conventional manner, as shown, so that theoscillator/timer 481 will respond to a signal at a first terminal(manufacturers pin 4) and provide an alternating output at a secondterminal (manufacturers pin 7) at a frequency proportional to themagnitude of the received signal. The first of these terminals isconnected through a voltage divider to the conductor 525 and the secondof these terminals is connected, via a conductor 483, to the clockterminal of a counter 485. Thus, the counter 485 continually runsthrough a sequence of numbers which are digitally expressed by voltagelevels at a plurality of output terminals collectively indicated at 551in FIGS. 24 and 25.

Referring now to FIG. 25, the terminals 551 are connected to the addressterminals of two type MM2716 PROMS, 487 and 489, forming a part of amodulator 506 illustrated in FIG. 22. The PROM 487 is programmed withsequential values of the sine of an angle as the angle varies from 0° to360° in steps equal to adjacent numbers appearing on the conductors 551which form the bus 551 illustrated in FIG. 22. Thus, in response to onecycle of counts generated by the counter 485, the PROM 487 provides asequence of values of the sine of an angle at its data terminals andsuch sequence of values are transmitted to a digital to analog converter491 on a bus 493. The PROM 489 is similarly programmed to produce asequence of values, defining the cosine of an angle from 0° to 360° inresponse to the counts appearing on the conductors 551 and such sequenceis transmitted to a digital to analog converter 495 on a bus 497. Thus,the output of the D/A converter 491 is a stepwise generated sinefunction and the output D/A converter 495 is a stepwise generated cosinefunction. The outputs of the D/A converters 491 and 495 are passedthrough impedence matching circuits 499 and 501 respectively, eachimpedence matching circuit 499, 501 being comprised of two seriallydisposed capacitors 503 and 505 and an interposed operational amplifier507, to identical low pass filters 509 and 511.

The output of the low pass filter 509 is passed to a variable resistor513, used to balance the signal levels provided to the coils 438 and440, and thence to one-half of a two section potentiometer 515. Theother half of the potentiometer 515 receives the output of the low passfilter 511. The two wiper arms of the two sections of the potentiometer515 are each provided to one input of a multiplier, the two multipliersbeing designated 517 and 519 in FIG. 25, and the second inputs of themultipliers 517 and 519 are connected to the conductors 549 of theencoder 472 shown in FIG. 23. Thus, the multipliers 517 and 519 produce,respectively, a sine wave output provided on an output conductor 562 anda cosine output provided on an output conductor 568 and such sine waveand cosine wave will have equal amplitudes that vary in accordance withthe magnitude of the signal provided by the D/A converter 479.

Returning to FIG. 22, the conductor 562 is connected to the inputterminal of a first power amplifier 564 and the conductor 568 issimilarly connected to the input terminal of a second power amplifier566. The output terminal of the first power amplifier 564 is connectedto the terminal 450 of the drive coil 438 and the ouput terminal of thesecond power amplifier 566 is similarly connected to the terminal 454 ofthe second drive coil 440.

As will be clear from the above description of the rotor control circuit458, the amplitude and frequency of the signal supplied to the coils 438and 440 can be controlled to have any desired relationship to themeasured value of any selected physical quantity. Once the frequencyrange has been selected and the sensor characterisitics have beendetermined, it is necessary only to program the PROM 474 to provide adigitally expressed value to the D/A converter 475 that will cause theoscillator/timer 481 to operate at a multiple of the desired frequencyequal to the total range of numbers expressible on the conductors 551.Similarly, once the maximum desired amplitude of the drive currents forthe coils 438 and 440 are known, along with the characteristics of thepower amplifiers 564 and 566, it is necessary only to program the PROM478 to provide, in conjunction with the D/A converter 479, anappropriate multiplying factor to the multipliers 517 and 519 on theconductor 549.

When the rotor suspension and rotation apparatus of the presentinvention is adapted to use as a blood pump, the capability of the rotorcontrol circuit 548 to control both the amplitude and frequency of thesignals supplied to the coils 438 and 440 in accordance with thepressure measured by the sensor 466 in the inlet passage 52 of the pump40 is used to cause the pump 40 to mimic the natural heart, and to do sowith minimum energy expenditure, as will now be described for the casein which the described eddy current drive system is used to rotate theimpellor 42.

The Frank-Starling effect specifies both the pressure differentialacross the heart and the flow rate of blood through the heart for arange of blood pressure at the inlet of the heart so that, for eachpressure in a known range, the flow rate and pressure differential thepump must produce to mimic the heart is known. In a centrifugal pump ofthe type shown in FIG. 1, the pressure differential is nearlyindependent of the flow rate, such pressure depending substantially onlyon the angular velocity of the impellor 42 of the pump 40. Additionally,maximum efficiency of operation of an eddy current motor, such as themotor incorporated into the pump 40, occurs when the operating point forthe motor is slightly above a breakover peak in a plot of deliveredtorque versus rotor angular velocity for any selected amplitude andfrequency of signals supplied to the stator of the motor. Thus, if theamplitude and frequency have selected values to provide an operatingcurve such as the curve 570 in FIG. 26, the maximum efficiency ofoperation will occur at the point 572. Similarly, if the amplitude andfrequency are selected to provide the operating curve 574, or the curve576, maximum efficiency of operation will occur at the point 578 or 580.As can be seen in FIG. 26, the angular velocity for which these maximumefficiency operating points occur are only slightly below angularvelocities corresponding to synchronous operation of the eddy currentmotor. Thus, to a good approximation, the frequency at which power is tobe supplied to the stator for any input pressure can be determined bymeasuring the angular velocity of the impellor for the pressuredifferential corresponding to the inlet pressure and dividing suchangular velocity by 2 pi. By measuring the necessary angular velocityfor a number of inlet pressure values within the range of pressures atthe inlet to the human heart to achieve the pressure differential valuesgiven by the Frank-Starling effect corresponding to such pressurevalues, a number of frequencies of the signals to be supplied to thestators for a number of inlet pressures that might occur in the humanheart are determined.

The Frank-Starling effect also provides the flow rate as a function ofinlet pressure so that the total amount of work that must be done on theblood to achieve a given flow rate at a given pressure differentialacross a pump, such work being the product of the flow rate and thepressure differential, is also determined for each pump inlet pressure.This work is also the product of the impellor angular velocity and thedelivered torque of the impellor so that the delivered torque is alsodetermined for each inlet pressure. To find the necessary amplitudes ofthe signals to be supplied to the stators for each inlet pressure, thetorque and angular velocity pairs for a number of inlet pressures areplotted on a graph such as shown in FIG. 26, as the points 572, 578 and580, and the amplitudes of signals to be supplied to the stators tocause an operating curve at each of the frequencies determined for theselected inlet pressure points to pass through these points areexperimentally determined. For example, the amplitude that yields thecurve 570 passing through the point 572, at the frequency determined forthe point 572 as described above for a given selected inlet pressure, isthe amplitude at which the stator is to be driven for the selectedpressure. By carrying out the procedure for several inlet pressures, amaximum efficiency curve 582 can be determined that is consistent withthe Frank-Starling effect of the natural heart and the frequency andamplitude of the rotor drive signals corresponding to several points onthe curve 582 will be known. The remaining amplitudes and frequenciescorresponding to other pressures can then be determined by extrapolationalong the curve 582. The amplitudes so determined are used to programthe memory device 478 and the frequencies so determined are used toprogram the memory device 474.

Operation of the Rotor Suspension and Rotation Apparatus

While it is believed that the operation of the rotor suspension androtation apparatus of the present invention will be clear from the abovedescription of the pump 40 that includes such apparatus, in that suchdescription includes the operation of each of the components of the pump40, it will nevertheless be useful to briefly summarize the operation ofthe pump 40 as a whole beginning with the operation of the magneticsuspension assembly.

When the pump 40 is placed in operation, the housing magnets 74 and 76will exert forces on the impellor magnets 78 and 80 that will cause therotation axis 60 of the impellor 42 to align itself with the supportaxis 48 of the housing 44. However, the support for the impellor 42provided by the permanent magnet impellor support assembly 68 isunstable with respect to axial movement of the impellor 42 along thehousing support axis 48. Thus, in the absence of the stabilization thatis provided by the electromagnet 70 and the electromagnet controlcircuit 72, the impellor 42 will move toward one of the inlet passages52 and 54 until the impellor 42 engages one of the flared portions ofthe bore 46 that forms the impellor chamber 50. In the presentinvention, impellor 42 is maintained in a suspended position within theimpellor chamber 50 as shown in FIG. 2 by forces that are exerted on theimpellor magnets 78 and 80 by the electromagnet 70 to continually drivethe impellor toward the control position in which the center of theimpellor is either at or near the null position of the impellor whichpermanent magnet forces thereon cancel.

Initially, it will be useful to consider the case in which the onlyaxial forces on the impellor are those provided by the permanent magnetimpellor support assembly 68 and the electromagnet 70, the latter forcebeing utilized only for stabilization purposes. If the impellor isinitially at the null position, pulses of infrared radiation that aredirected across the two inlet passages 52 and 54 by the light emittingdiodes 158 and 160 will be equally shaded so that the phototransistors170 and 172 of the infrared receivers 178 and 180 will be equallyilluminated. Accordingly, each time the astable multivibrator 120produces an electrical pulse to cause the light emitting diodes todirect an infrared pulse across the inlet passages 52 and 54, theinfrared receivers 178 and 180 will deliver equal size electrical pulsesto the difference amplifier 196 so that the output of the differenceamplifier 196 will be zero for each pulse produced by the multivibrator120. Between pulses, the light emitting diodes 158 and 160 do not emitso that the phototransistors 174 and 176 are not illuminated with theresult that, between pulses, the difference amplifier receives nosignals at its inputs and again produces no output. Thus, so long as theimpellor 42 is located at the null position thereof, the differenceamplifier will have a null output which is transmitted to the integrator208. Thus, for each set of six pulses produced by the astablemultivibrator to cause the integrator 208 to carry out an integrationcycle, the integrator 208 will be receiving no input and will store nocharge on the capacitor 216 thereof Thus, when the integrator 208 isconnected to the sample and hold circuit by the closure of the switch234 that has been described above, no charge will be transferred fromthe integrator to the sample and hold circuit so that the capacitor 232of the sample and hold circuit will remain uncharged. Thus, the firstcontroller 318 receives a null control signal which is matched by a nullcontrol signal provided by the summing circuit comprised of theresistors 336 and 338 with the result that the first controller 318delivers a null signal to the power amplifier 322. In response to thisnull signal, the power amplifier 322 will pass no current through theelectromagnet 70.

Should the impellor 42 now become displaced from the null position, theshading of one of the phototransistors 174, 176 by the impellor 42 willbe increased while the shading of the other phototransistors 174, 176will be decreased. Thus, with every electrical pulse produced by theastable multivibrator 120 to give rise to the pulses of infraredradiation directed across the passages 52, 54, unequal signals willreach the difference amplifier from the infrared receivers 178, 180which include the phototransistors 170, 172 Thus, for every pulseproduced by the astable multivibrator 120, the difference amplifier 196will provide an electrical pulse to the integrator 208 and the magnitudeand polarity of such pulse will depend upon the distance the impellor 42has been shifted from the null position and the direction of such shiftFour of every six of these pulses are integrated by the integrator 208and, at the conclusion of such integration, the charge stored on thecapacitor 216 of the integrator as the result of such integration istransferred to the sample and hold circuit 228. The charge that istransferred to the sample and hold circuit 228 is then stored thereinand utilized to control the first controller for the next six pulsesproduced by the astable multivibrator 120. During the first two of thesepulses, integrator 208 is reset to again integrate the signal from thedifference amplifier 196 for the remaining four pulses immediatelypreceding the transfer of a new charge to the sample and hold circuitThus, for every six electrical pulses produced by the astablemultivibrator 120, the sample and hold circuit 228 will contain acharge, determined from the preceding four pulses produced by theastable multivibrator 120, that is indicative of the location of theimpellor 42 with respect to the null position during such four precedingpulses. It will be noticed that the sample and hold circuit 228 stores acharge for a full six pulses rather than just the four pulses whichproduce the charge so that no time period occurs in which the sample andthe hold circuit does not store a charge that is related to the positionof the impellor 42 in the impellor chamber 50.

The sample and hold circuit 228 provides a signal proportional to thestored charge to the first controller 318 and the first controller 318provides an output signal to the power amplifier 322 which isproportional to the difference between the signal received from thesample and hold circuit 228 and a signal received from the secondcontroller 320. The second controller 320 is connected to the output ofthe first controller 318 and is adjusted via the variable resistor 366thereof so that, in the absence of a persistent direct current componentin the output of the first controller 318, the signal provided by thesecond controller 320 to the first controller 344 will be a null signal.Thus, so long as no persistent DC component arises in the output of thecontroller 318, the controller 318 will provide a signal to the poweramplifier 322 which is indicative of the position of the impellor 42with respect to the null position thereof. In response, the poweramplifier 322 passes a current through the electromagnet 70 to produce amagnetic field that exerts a force on the impellor magnets 78 and 80 todrive the impellor back toward the null position in which the impellor42 is centered in the impellor chamber 50.

Should an additional axial force now be exerted on the impellor 42, suchforce will cause the impellor 42 to shift away from the null position inthe direction of the force so that unequal shading of thephototransistors 170 and 172, persistently in favor of one of thephototransistors, will occur. In the absence of the second controller,the electromagnet control circuit would operate as has been describedabove to pass a current through the electromagnet 70 tending to drivethe impellor 42 back toward the null position. However, since theimpellor 42 is now systematically displaced from the null position, thecurrent passed through the electromagnet 70 will have a direct currentcomponent that will result in the large expenditure of energy by theelectromagnet control circuit 72. The second controller 320 preventsthis large expenditure of energy by detecting persistent signals in theoutput of the first controller 318 and, in response to the presence ofsuch signals, providing a new reference signal to the first controller318 against which the signal from the sample and hold circuit 228 iscompared. Thus, the effect of the second controller 320 is to cause thefirst controller 318 to deliver a null signal to the power amplifier 322for a condition in which the signal received by the first controller 318from the sample and hold circuit 228 is not a null signal. Inparticular, the second controller 320 automatically causes the signalfrom the sample and hold circuit 228 for which the first controlleroutput is a null signal to be the signal that is produced by the sampleand hold circuit 228 when the impellor 42 is displaced from the nullposition to a control position at which the permanent magnet force onthe impellor 42 just balances the additional axial force on the impellor42. Thus, the electromagnet control circuit 72 and the electromagnet 70maintain the impellor 42 at the control position which, in the absenceof non-permanent magnet axial forces on the impellor 42, is the nullposition of the impellor 42 with the least expenditure of energy by theelectromagnet control system 72 by using the permanent magnets of thepermanent magnet impellor support assembly 68 to support the impellor 42in the housing 44 while the current passed through the electromagnet 70is used only for stabilization of the support of the impellor 42 withinthe housing 44.

In some applications of the magnetic suspension and rotation apparatusof the present invention, no static axial forces will be exerted on thesuspended and rotated rotor other than the forces exerted thereon by thepermanent magnet rotor support assembly 68. In these applications, thecontrol position will coincide with the null position and the secondcontroller 320 can be deleted from the electromagnet control circuit 72.The non-inverting input terminal of the operational amplifier 326 of thefirst controller 318 is connected directly to the wiper arm of the zeroadjustment potentiometer 342 in such applications.

While the impellor 42 is so suspended, the pressure sensor 266, in thecase of a blood pump, measures the fluid pressure in the first inletpassage 52 of the pump 40 and provides an analog signal proportional tosuch pressure to the A/D converter 468 which, in turn, provides adigitized representation of the magnitude of the pressure to the encoder472. This representation is utilized in the memory device 474 to providea code to the oscillator 476 that determines the frequency necessary tobe supplied to the coils 438 and 440 disposed about the impellor 42 toform an eddy current motor with the shorting ring 424 that is mounted onthe impellor 42 to cause, for a selected amplitude of the signalprovided to the coils 438 and 440, the impellor 42 to rotate at a speedthat will cause the flow of blood through the pump 40 to duplicate theflow rate of the natural heart at the pressure sensed by the sensor 466.The memory device 478 of the encoder 472 receives the output of thememory device 474 and is programmed to cause the modulator 506, whichreceives the oscillating signal produced by the oscillator 476, toprovide the appropriate amplitude corresponding to such frequency sothat, for each pressure sensed by the sensor 466, the flow rate of bloodthrough the pump 40 will be the same as the flow rate produced by thenatural heart for the same pressure at the inlet of the natural heart.

Description of FIGS. 27 and 28

FIGS. 27 and 28 illustrate a modification of the pump impellor,designated 42A in such Figures, that is particularly useful in highpressure pumping applications of a pump utilizing the magnetic rotorsuspension and rotation apparatus of the present invention or inapplications requiring a small size pump. The impellor 42A is comprisedof an impellor body 570 that has the same form as the impellor 42; thatis, the impellor 42A has first and second conical end portions, 572 and574 respectively, that are joined at their bases in the same manner thatthe end portions 62 and 64 of the impellor 42 are joined. (The shortingring and impellor magnets, not shown in FIGS. 27 and 28, are mounted onthe impellor body 570 of the impellor 42A in the same manner and for thesame purpose that the shorting ring 424 and impellor magnets 78, 80 aremounted on the impellor 42. Similarly, the impellor body 570 has acavity that is symmetrically positioned with respect to the rotationaxis 576 of the impellor 42A and with respect to a midplane at which thebases of the end portions 572 and 574 are joined so that the center ofgravity of the impellor and portions of the suspension and rotor driveassemblies mounted thereon will be located at the center of buoyancy ofthe impellor 42A for the same reasons that have been discussed abovewith respect to the impellor 42.) In order to enable a pump comprisingthe impellor 42A to be utilized in high pressure pumping applications orto be made small without loss of pumping capacity, a plurality of curvedvanes 578, only one of which has been numerically designated in thedrawings, are disposed on each of the end portions of the impellor body570 to extend generally from the center of the impellor body 570 topositions near the apices of the end portion 572 and 574 of the impellorbody 570. The vanes 578 provide a stronger mechanical coupling betweenthe rotor 42A than the viscous coupling provided by the surface of therotor 42 so that a larger pressure differential can generally beestablished between the inlet and outlet passages of a pump containingthe impellor 42A than can be established with a pump containing theimpellor 42 or the same flow rate can be established in a smaller pump.In order to minimize damage to blood that might be occasioned by thevanes 578 should a pump including the impellor 42A be used in bloodpumping operations, the vanes 578 are positioned along streamlines ofblood through the pump for an average flow velocity of blood through thepump. Similarly, sharp edges are avoided on the vanes to prevent sharpstresses in the microenvironment of the blood components.

Description of FIG. 29

FIG. 29 illustrates a third embodiment of the impellor, designated 42B,that is also suitable for high pressure pumping applications of themagnetic rotor suspension and rotation apparatus of the presentinvention and for applications requiring minimum pump dimensions. Theimpellor 42B comprises an impellor body 580 that is hollow for specificgravity matching between the impellor 42B and a liquid pumped by theimpellor 42B, the impellor body 580 having conical first and second endportions, 582 and 584 respectively, that are joined at their bases andhave apices along the rotation axis 586 of the impellor 42D. In additionto the impellor body 580, the impellor 42B also includes two hollow,frusto-conical duct-forming shells 588 and 590 that are mounted on theimpellor body 582 to extend coaxially about the end portions 582 and 584respectively thereof. The coaxial disposition of the duct-formingmembers 588, 590 about the impellor body end portions 582, 584 formsducts 592, 594 through the impellor 42B from the ends 596, 598 of theimpellor 42B to the center of the impellor 42B such that the ducts 592,594 extend about the impellor body 580 and open into the groove 58 (FIG.3) that extends circumferentially about the impellor 42B when theimpellor 42B is suspended in the housing 44. Webs 600 in the ducts 592,594 are used to mount the duct-forming members 588 and 590 on theimpellor body 580.

In the impellor 42B, the impellor magnets take the form of rings 602 and604 that are mounted in the duct-forming members 588 and 590respectively near the ends 596 and 598 of the impellor 42B. Like theimpellor magnets 78 and 80 of the impellor 42, the impellor magnets 602and 604 are axially magnetized; that is, magnetized parallel to therotation axis 586 of the impellor 42B, to provide the same permanentmagnet support for the impellor 42B that the impellor magnets 78 and 80provide for the impellor 42. Additionally, the shorting ring, indicatedat 606 in FIG. 29, that is used to convert the impellor 42B into therotor of an eddy current motor, is mounted on the duct-forming members588 and 590. In order to provide for the circumferenctial opening of theducts 592 and 594 about the central portions of the circumference of theimpellor 42B, the shorting ring 606 is constructed in two parts,indicated at 608 and 610 in FIG. 29, each of the parts 608 and 610 beingmounted on one of the duct-forming members 588, 590 adjacent thecircumferential opening of the ducts 592, 594 about the center of theimpellor 42B.

The construction of the impellor 42B provides a stronger impellor-pumpedfluid coupling by enhancing the viscous coupling between the impellor42B and the liquid being pumped. That is, by forming the ducts 592, 594through the impellor 42B, the impellor 42B presents a greater surfacearea in contact with the liquid than is presented by the impellor 42.Additionally, the webs 600 enhance the mechanical coupling between theimpellor 42B and a liquid being pumped and the webs 600 can be curvedalong stream lines of liquid through the ducts 592, 594 for a selectedangular velocity of the impellor 42B to limit mechanical working of theliquid when the impellor 42B is used in blood pumping applicationsFurther enhanced mechanical coupling between the impellor 42B and liquidbeing pumped can be provided by vanes 612 on the radially outermostsurface 614 of the duct-forming member 588 and vanes 616 on the radiallyoutermost surface 618 of the duct-forming member 590. Curvature of thevanes 612 and 616 can similarly be used to limit mechanical damage toblood when the impellor 42B is used in blood pumping applications.

Description of FIG. 30

Referring now to FIG. 30, shown therein and designated by the referencenumeral 42C is a fourth embodiment of an impellor suitable for use inpumping applications of the rotor suspension and rotation apparatus ofthe present invention. Like the impellor 42B, the impellor 42C iscomprised of: a hollow impellor body 620, having first and secondconical end portions 622 and 624 respectively that are joined at theirbases and have apices along the rotation axis 626 of the impellor 42C;and hollow frusto-conical duct-forming shells 628 and 630 that arepositioned coaxially about the end portions of the impellor body 620 toform annular ducts 632, 634 that extend from the ends 636, 638 of theimpellor 42C to open circumferentially about the center of the impellor42C. As in the case of the impellor 42B, the shorting ring 640 thatextends about central portions of the impellor 42C to convert theimpellor 42C into the rotor of an eddy current motor is constructed intwo parts, 642 and 644, with one part being mounted on each of theduct-forming shells 628, 630. Similarly, in the impellor 42C, theimpellor magnets 646, 648 have the form of axially magnetized rings thatare mounted in the duct-forming shells 628 and 630 respectively.

In addition to the impellor body 620 and the duct-forming shells 628 and630, the impellor 42C further comprises three hollow, frusto-conicalintermediate shells 650-654 mounted in the duct 632 to extend coaxiallyabout the first end portion 622 of the impellor body 620 and threehollow, frusto-conical shells 656-660 similarly mounted within the duct634 to extend coaxially about the second end portion 624 of the impellorbody 620. A web assembly 662 comprised of a plurality of webs (notnumerically designated in the drawings) is used to mount the shells 628,630 and 650-660 on the impellor body 620.

The impellor 42C has a large area in contact with a liquid being pumpedby a pump including the impellor 42C to provide an enhanced viscouscoupling between the impellor 42C and such liquid, thereby adapting theimpellor 42C to high pressure pumping applications or, equivalently, topumping applications in which the size of the pump is to be minimized.

Description of FIGS. 31 and 32

FIGS. 31 and 32 illustrate a second embodiment of a pump, generallydesignated by the numeral 664 in such Figures, that includes themagnetic rotor suspension and rotation apparatus of the presentinvention. The pump 664 comprises a housing 666 having a bore 668 formedtherethrough and an impellor 670 mounted in central portions of the bore668 to force a fluid axially through the bore 668. Thus, centralportions of the bore 668 form an impellor chamber (not numericallydesignated in FIGS. 31 and 32) and end portions of the bore 668,intersecting ends 672 and 674 of the housing 666, form inlet and outletpassages 676 and 678 respectively, into the impellor chamber.

In the pump 664, the impellor 670 has the general form of a circular rodhaving tapered ends with the rotation axis (not designated in FIG. 31)of the impellor 670 extending longitudinally between the ends 680 and682 of the impellor 670. In operation, the impellor 670 is supportedalong the axis 684 of the bore 668, the axis 684 forming the supportaxis of the housing 666 that is equivalent to the support axis 48 of thehousing 40. The support of the impellor 670 is accomplished, in the samemanner that the support of the impellor 42 is accomplished in the pump40, via a permanent magnet impellor support assembly 686 that iscomprised of two housing magnets 688 and 690 constructed, positioned,and magnetized in the manner of the housing magnets 74 and 76, and tworing-shaped, axially magnetized impellor magnets 692 and 694 that arepositioned on the impellor 670 in relation to the positioning of thehousing magnets 688, 690 in the same way that the impellor magnets 78and 80 are positioned with respect to the housing magnets 74 and 76 inthe pump 40. The permanent magnet impellor support assembly 686 thustends to position the impellor 670 in the housing 666 in the same mannerthat the permanent magnet impellor support assembly 68 positions theimpellor 42 in the housing 44 of the pump 40; that is, the permanentmagnets 688-694 tend to align the rotation axis from the impellor 670with the housing axis 684 while tending to drive the impellor 670 awayfrom a magnetic null position located axially midway between the housingmagnets 688 and 690 on the housing axis 684.

A plurality of vanes 696 are formed on the surface 698 of the impellor670 to curve about the impellor 670 nearly the length thereof so that,when the impellor is rotated in the direction 700 indicated in FIG. 32,the impellor 670 will drive a liquid from the inlet passage 676 to theoutlet passage 678 in the direction indicated by the arrows 702 and 704in FIG. 31.

In order to stabilize the support of the impellor 670 provided by thepermanent magnet impellor support assembly 686, the pump 664 includes anelectromagnet 706, constructed and positioned substantially identicallyto the construction and position of the electromagnet 70 of the pump 40,and an electromagnet control circuit that is identical to theelectromagnet control circuit 72. In order to mount the light emittingdiodes 158 and 160 of the infrared transmitter 142 of the electromagnetcontrol circuit 72 on the housing 666 of the pump 664, sockets 708 and710 are formed in the inside wall of the housing 666 provided by thebore 668 and, similarly, in order to mount the phototransistors 174 ofthe two infrared receivers 178 and 180 on the housing 666, sockets 712and 714 are formed coaxially with and in diametric opposition to thesockets 708 and 710. In the pump 664, a reaction force tending to drivethe impellor 670 toward the end 672 of the housing 666 from which liquidenters the bore 668 will be exerted on the impellor 670 because of theaxial nature of the flow of the liquid through the bore 668. Thisreaction force is countered, by the action of the second controller 320that has been discussed above, by a shift in position of the impellor670 to a control position which is slightly upstream of the nullposition at which the permanent magnet forces on the impellor 670cancel.

Rotation of the impellor 670 is effected by a shorting ring 716 thatextends about the center of the impellor 670 and a stator 718 mounted inthe housing 666 to extend about the shorting ring 716. The stator 718 iscomprised of a ferromagnetic ring 720 positioned concentrically with theshorting ring 716 and having four radially inwardly extendingprojections 722 formed thereon. A coil 723 is wound on two diametricallyopposed projections 722 and a similar coil 724 is wound onto remainingtwo diametrically opposed projections 724 and the coils 723 and 724 aredriven by a rotation control circuit that is identical to the rotationcontrol circuit 458 shown in FIGS. 22-25. The mounting of the pressuresensor 466 of the rotation control circuit 458 in the pump 664 is via asocket 726 in the inlet passage 676 of the housing 666 as shown in FIG.31.

The impellor 670 is formed symmetrically so that the center of gravityof the impellor and portions of the magnetic suspension assembly andimpellor drive assembly mounted thereon will be located at the center ofbuoyancy of the impellor 670 and a cavity 729 is formed in the center ofthe impellor 670 to match the average specific gravity of the impellor670 and portions of the magnetic suspension assembly and impellor driveassembly thereon to the specific gravity of the liquid that is pumped bythe pump 664 for the reason that has been discussed above.

Description of FIG. 33

Referring now to FIG. 33, shown therein and designated by the numeral728, is another embodiment of a pump constructed in accordance with thepresent invention to include a magnetic rotor suspension and rotationapparatus. The pump 728 comprises a housing 730 that is similar to thehousing 666 of the pump 664, housings 630 and 666 differing primarily inthe manner in which a bore 732 is formed through the housing 730 and inthe addition of flow control structures in the bore 732. In the housing730, the portions of the bore 732 that form an inlet passage 734 andoutlet passage 736 to, and from, the central portion of the bore 732that forms an impellor chamber are formed, respectively, about an inletflow axis 738 and an outlet flow axis 740 that are not coincident withthe housing support axis 742 along which the rotation axis of the pumpimpellor (not numerically indicated in FIG. 33), extends. Rather, theinlet flow axis 738 and the outlet flow axis 740 each intersect thehousing support axis 742 at an obtuse angle so that the inlet and outletpassages 734 and 736 are both canted to one side of the housing 730,such side being the same for both passages 734 and 736. The canting ofthe inlet and outlet passages 734 and 736 respectively provides the pump728 with a shape that is similar to the shape of the human heart tofacilitate positioning of the pump 728 within the chest and furthertends to eliminate formation of vortical flow patterns in a fluid pumpedby the pump 728 to thus reduce the energy required to rotate theimpellor 742. Vortical flow suppression is also affected by a flowcontrol vane 746 that is formed integrally with the housing 730 withinthe inlet passage 734 parallel to the inlet flow axis 738 and an outletflow control vane 748 formed integrally with the housing 730 within theoutlet passage 736 to parallel the outlet flow axis 738.

The impellor 744 in the pump 728 differs from the impellor 670 of thepump 664 in that the impellor 744 has the form of a circular ring havingcoaxial inner and outer peripheral surfaces, 750 and 752 respectively,centered on the rotation axis (not numerically designated in FIG. 33) ofthe impellor 744. A plurality of curved vanes 754 are formed integrallywith the impellor 744, on the inner peripheral surface 750 thereof, sothat a fluid can be forced through the pump 728, from the inlet passage734 to the outlet passage 736, by rotating the impellor 744 about therotation axis thereof.

The pump 728 is provided with a magnetic suspension assembly that isidentical to the magnetic suspension assembly of the pump 664 so thatsuch magnetic suspension assembly need not be again described herein.Rather, it will suffice to numerically identify the portions of themagnetic suspension assembly that are mounted on the housing andimpellor of the pump 728. Such portions of the magnetic suspensionassembly for the pump 728 are: ring shaped permanent housing magnets 756and 758; ring shaped permanent impellor magnets 760 and 762; anelectromagnet 764; two light emitting diodes 766 and 768 disposed insockets 770 and 772 respectively at opposite ends of the impellorchamber; and two phototransistors 774 and 776 disposed in sockets 778and 780 that are coaxially with, and in diametric opposition across theimpellor chamber to, the sockets 770 and 772.

The rotation rate of the impellor 744 can be controlled in relation tothe pressure at the inlet passage 734 of the pump 728 in accordance withthe Frank-Starling effect and a pressure sensor 782 is mounted in asocket 784 formed in the wall of the inlet passage 734 for this purpose.The rotation of the impellor 744 is then effected via a shorting ring785 mounted on the impellor 744 to extend about central portions thereofand a stator 787 that is identical to the stator 718 of the pump 664shown in FIG. 31. Control of the rotation rate of the impellor 744 sothat the pumping rate of the pump 728 will mimic the pumpingcharacteristics of the natural heart is then effected with a rotorcontrol circuit such as the rotor control circuit 458 shown in FIGS.22-25.

Description of FIG. 34

FIG. 34 illustrates another embodiment of a pump, designated by thegeneral reference numeral 786, that has an impellor 788 suspended androtated by the magnetic rotor suspension and rotation apparatusconstructed in accordance with the present invention. The pump 786 isparticularly suited for use as a heart assist device.

The pump 786 is comprised of a housing 790, having a bore 792 formedtherethrough, and portions of the bore 792 near one end 794 of thehousing 790 provide an impellor chamber (not numerically designated inFIG. 34) in which the impellor 788 is disposed. In particular, theimpellor 788 is displaced generally from central portions of the bore792 toward the end of the housing 790 that is intersected by the outletpassage 796 of the pump 786. The portion of the bore 792 forming aninlet passage 788 is elongated and an annular restriction 800 is formedin the inlet passage 798 to provide part of a valve that automaticallycloses the bore 792 should the pump 786 cease to operate for someunforseeable reason. Thus, where the pump 786 is used as a heart assistdevice, as will be discussed below, a cessation of the operation of thepump 786 will not result in a back flow through the bore 792 as theheart continues to beat.

The impellor 788 in the pump 786 has a ring-shaped portion 802 that issubstantially identical to the impellor 744 of the pump 728 and curvedvanes 804 formed integrally with the portion 802 on the inner peripheralsurface 806 of such portion 802 effect the pumping of liquid through theportion 802 in response to rotation of the impellor 788 about a rotationaxis extending axially through the impellor 788 along the center of thering shaped portion 802. The vanes 804 extend axially from the portion802 of the impellor 788 to support a valve member 808 adjacent theannular restriction 800 formed in the inlet passage 798 and the valvemember 808 has a nose portion 810 that is shaped to mate with therestriction 800 so that, should the pump 786 cease to operate at a timethat the pump 786 is assisting a natural heart, blood pressure exertedby the heart will force the nose portion 810 of the valve member 808into the restriction 800 to prevent back flow through the pump 786.

In order to accomodate the automatic valve provided by the restriction800 and the valve member 808, the inlet passage 798 of the valve 786extends axially from the impellor chamber in which the ring shapedportion 802 of the impellor 788 is disposed; that is, the inlet passage798 is formed about the housing support axis 812 shown in FIG. 34. Theoutlet passage 796, however, is preferably canted with respect to thehousing support axis in the manner that the outlet passage 736 is cantedand for the same reasons. Thus, the outlet passage 792 is centered on anoutlet flow axis 814 that makes an obtuse angle with the housing supportaxis 812. Similarly, an outlet flow control vane 816 is integrallyformed with the housing 790 to extend axially through the outlet passage796 parallel to the outlet flow axis 814.

The magnetic suspension assembly for the pump 786 differs from themagnetic suspension assembly for the pump 728 in several respects. Inaddition to the inclusion in the pump 786 of permanent housing magnets818 and 820 and permanent impellor magnets 822 and 824, which areshaped, positioned, and magnetized in a manner identical to the shaping,positioning and magnetization of the magnets 756-762 of the pump 728,the pump 786 also comprises ring-shaped impellor magnets 826 and 827that are mounted in the valve member 808 and ring-shaped housing magnets828 and 829 that are mounted in the housing 790 to extend about theinlet passage 798. As indicated in FIG. 34, the magnets 826 and 828 aredisposed concentrically and are radially magnetized in oppositedirections to provide stable radial support of the valve member 808 andunstable axial support. The magnets 827 and 829 are axially magnetizedin opposite directions, as shown, and are positioned and dimensioned toprovide a small axial force on the impellor 788 tending to drive thevalve member 808 into the restriction 800. Thus, should the pump 786cease to operate, the magnets 827 and 829 will reinforce the tendency ofthe magnets 808-824 to automatically close the inlet 798 of the pump 786to prevent the formation of short circuit between the inlet and outletof the natural heart with which the pump 786 might be used.

Because of the shape of the impellor 788 of the pump 786, it isconvenient to use a modified electromagnet control circuit that includesonly one infrared receiver and for which the infrared transmitterincludes only one light emitting diode, such light emitting diode,indicated at 834 in FIG. 34, being positioned in the housing 790adjacent the outlet passage 792. (The infrared receiver that is includedin the electromagnet control circuit provided for the pump 786 willinclude a phototransistor that has not been shown in FIG. 34 but ispositioned in diametric opposition to the light emitting diode 834 inthe manner of phototransistors and light emitting diodes in previouslydescribed embodiments of pumps that incorporate the magnetic impellorsuspension and rotation apparatus of the present invention.) When onlyone infrared receiver is utilized in the stabilization of the support ofan impellor, or rotor, that is suspended in accordance with theprinciples of the present invention, the conductor 194 in FIG. 12leading to the inverting input of the operational amplifier 198 of thedifference amplifier of the electromagnet control circuit is connectedto the circuit ground for the electromagnet control circuit and the zeroadjustment potentiometer 342 in the first controller shown in FIG. 16 isadjusted so that the signal at the output terminal of the differenceamplifier 326 of the first controller 318 will be zero when theimpellor, or rotor, being stabilized is at the null position thereof inthe absence of axial forces on the impellor, or rotor, not arising frompermanent magnets used to support such impellor or rotor.

The impellor 788 can be rotated via a shorting ring 836 mounted in theimpellor 788, a stator (not numerically designated in FIG. 34) mountedin the housing 790 in the same manner that the stator 718 in FIG. 32 ismounted in the housing 666 of the pump 664, and a rotor control circuitthat is identical to the rotor control circuit 458 shown in FIGS. 22-25.To provide for the control of the rotation speed of the impellor 788 ofthe pump 786, a socket 838 is formed in the wall of the inlet passage798 to receive the pressure sensor 466 of such rotor control circuit458.

Description of FIGS. 35 and 36

FIGS. 35 and 36 illustrate a second embodiment of a rotor drive assemblythat can be used to rotate a rotor or impellor that is magneticallysuspended in accordance with the principles of the present invention. InFIG. 35, the impellor has been designated by the numeral 840 and FIG. 35contemplates that the impellor 840 will be magnetically suspended withina housing 842 and rotated via an eddy current drive in a manner similarto the rotation of the impellors that have been previously discussed.Thus, a shorting ring 844 is included in the impellor 840 to extendabout central portions of the impellor 840. However, instead ofcomprising a stator having four radially inwardly directed projectionson a ring portion concentric with the shorting ring as previouslydiscussed, the rotor drive assembly illustrated in FIGS. 35 and 36 iscomprised of a stator 846 that includes a ring 848 positionedconcentrically with the shorting ring 844 and having six equally spaced,radially inwardly extending projections 850. Windings 858, 860 and 862are each wrapped on one pair of diametrically opposed projections 850and a modified rotor control circuit is used to pass currents throughthe stator windings 858-862.

Initially, in order to provide an eddy current drive with three statorwindings, the windings are connected together in a star connection asindicated by the connection of each of the windings 858-862 to thegrounded conductor 864 in FIG. 36. The stator windings are then drivenby oscillating signals having the same amplitudes and frequencies butout of phase, from one stator winding to the next, by 60° . In FIG. 36,these signals are provided by power amplifiers 866-870 that areconnected to the three stator windings 858-862 respectively and areconstructed in the manner of the power stage 372 of the power amplifier322 of the suspension circuit 72. As in the case of the rotor controlcircuit 458, each of the power amplifiers 866-870 is driven by amodulator that is constructed in the manner shown in FIG. 25, suchmodulators being indicated for the power amplifiers 866-870 at 872-876respectively in FIG. 36. Thus, the rotation of the impellor 840 in FIG.35, and the control of such rotation in accordance with a preselectedrelationship between the angular velocity of the impellor 840 and thevalue of a measured physical quantity, can be achieved by supplying anappropriate, digitally expressed amplitude control signal to themultiplying A/D convertor of each of the modulators 872-876, via buses878-882 shown in FIG. 36, and by supplying appropriately phasedoscillating signals to the reference input terminals of the convertorsof the modulators 872-876 on conducting paths 884-888 shown in FIG. 36.

The supply of digitally expressed amplitude control signals to themodulators 872-876 is effected in the same manner that amplitude controlsignals are supplied to the modulators 506 and 508 of the rotor controlcircuit 458. That is, the amplitude control signals are supplied on thebuses 878-882 directly from an encoder (not shown in FIG. 36 but havingthe same form as the encoder 472 shown in FIG. 23) that receives signalsfrom a sensor (not shown in FIG. 36) via an A/D convertor (not shown inFIG. 36). The encoder used to supply these amplitude control signals isalso used to fix the frequency of oscillation of an oscillator (notshown in FIG. 36 but constructed in the manner of the oscillator 476shown in FIG. 24) from which the alternating signals on the conductingpaths 884-888 are derived as will now be discussed.

One output of the oscillator from which the signals on the paths 884-888are derived is connected, via a conductor 890, to the clock terminal(not shown) of a binary counter 892, having a plurality of outputterminals (not shown) at which a binary number can be expressed as apattern of high and low voltages, so that the binary number at theoutput terminals of the counter 892 is incremented for each cycle of thesignal received on the path 890. The output terminals of the counter 892are connected, via buses 894-898, to three function storage devicesindicated at 900-904 in FIG. 36. The function storage devices 900-904are conveniently PROMS to the address terminals of which are connectedthe buses 894-898 respectively. The function storage devices 900-904 areprogrammed to provide, at data terminals thereof, a sequence of valuesin one cycle of a sine curve in response to one complete cycle of binarynumbers produced by the counter 892, the sequence of values of the sinecurve being divided into a number of equal increments that is equal tothe maximum number of values that can be expressed as a binary number atthe output terminals of the counter 892. Thus, the binary numbers at thedata terminals of the function storage devices 900-904 will run througha sequence of values of a sine curve each time the counter 892 runsthrough a complete cycle of numbers beginning with all output terminalsof the counter 892 being at a low voltage and ending with all outputterminals of the counter 892 being at a high voltage. Moreover, theprogramming of the function storage devices 900-904 is correlated sothat the first number appearing at the data terminals of the functionstorage device 900 as the counter 892 runs through one complete cyclebeginning with the binarily expressed number 0 is the sine of 0° ; thefirst number to appear at the data terminals of the function storagedevice 902 as the counter 892 runs through a cycle is the binaryexpression of the sine of 60° ; and the first number to appear at thedata terminals of the function storage device 904 as the counter 892runs through a cycle is the binary expression of the sine of 120° .Thus, each time the counter 892 runs through one complete cycle ofnumbers beginning with a binarily expressed 0, the function storagedevices 900-904 will run through a series of numbers corresponding toequal increments in the functions sin (360° n/N), sin (360° n/N+60° ),and sin (360° n/n+120° ) where n is the number expressed at the outputterminals of the counter 892 and N is the maximum number expressible bythe counter 892. The data terminals of the function storage devices900-904 are connected to the inputs of D/A convertors 906-910respectively via buses 912-916 respectively so that step wiseapproximations of the functions sin X, sin (X+60° ), and sin (X+120° )are produced at output terminals (not shown) of the D/A convertors906-910 each time the counter 892 runs through one complete cycle ofnumbers beginning with a binarily expressed 0. The outputs of the D/Aconvertors 906-910 are provided, on signal paths 924-928 respectively,to filters 918-922 respectively and the outputs of the filters aresupplied on the signal paths 884-888 to the modulators 872-876. Thus,the reference input terminals of the multiplying D/A convertors of themodulators 872-876 are supplied with sine wave signals having the sameamplitudes and frequencies but out of phase by 60° from one signal toanother to provide appropriate signals for driving the stator windings858-862 to cause eddy currents in the shorting ring 844 to rotate theimpellor 840.

Description of FIG. 37

FIG. 37 has been included to indicate, schematically, the manner inwhich an artificial heart, designated by the numeral 931, can beassembled using pumps including the magnetic rotor suspension androtation apparatus of the present invention and connected into thecirculatory system of a human patient. For such application of theinvention, two pumps, 930 and 932, are used, each of the pumps 930 and932 having its own magnetic suspension assembly and its own impellordrive assembly constructed as has been discussed above. One powersupply, comprised of a plurality of rechargeable batteries, implanted inthe body along with the pumps 930, 932, can be used to operate bothpumps and it is contemplated that the batteries of the power supply canbe periodically recharged via an induction coil implanted in the body asdisclosed in the aforementioned U.S. Pat. application, Ser. No. 245,007.

The pumps 930 and 932 can be pumps of the type illustrated in FIGS. 1-3and an advantage of the use of such pumps is the capability such pumpsprovide for matching the average specific gravity of the impellors ofthe pumps to the specific gravity of blood as discussed above. With suchmatching, and the construction of the pump impellors so that the centersof gravity of the pump impellors are located at the centers of buoyancyof the impellors, and the impellors of the pumps 930, 932 areeffectively portions of the blood being pumped insofar as gravitationaland buoyant forces are concerned and insofar as inertial effects arisingfrom accelerations of the pumps 930 and 932 are concerned. Thus, no workneed be done by the magnetic suspension assembly as the result ofmovements of the person receiving an artificial heart comprised of thepumps 930 and 932. Moreover, the energy required to operate the pumps930 and 932 is completely independent of the orientations of the pumps930, 932 in the chest cavity so that geometrical considerations such asthe attachment of the pumps 930, 932 to the circulatory system and thefitting of the pumps 930, 932 in the position normally occupied by theheart can control the positioning of the pumps 930, 932 in the body.Convenient orientations of the pumps have been shown in FIG. 37.

In the use of two pumps, such as the pumps 930 and 932, as an artificialheart, the pumps can be of different sizes and different powercapabilities corresponding to the different sizes and pumpingcapabilities of the two sides of the heart. Such differences have beencontemplated in FIG. 32 in which the pump 930 is illustrated as beingsmaller than the pump 932. In this case, the smaller pump 930 isutilized to provide a flow of blood into the pulmonary artery 934 towhich the outlet 936 of the pump 930 is connected via a length of tubing938 constructed of a plastic that is compatible with blood. The twoinlets of the pump 930 are inserted into, and secured to, the superiorvena cava 940 and the inferior vena cava 942 so that the pump 930occupies a position normally occupied by the right atrium of the naturalheart. The pump 932 is positioned at the location normally occupied bythe ventricles of the heart and the inlets of the pump 932 are connectedto a T-fitting 944 via tubes 946 and 948. FIG. 37 contemplates that theleft atrium of the natural heart will be left in the chest cavity of theperson receiving the artificial heart and the T-fitting 944 is connectedto the left atrium by means of a length of tubing 950. The outlet 952 ofthe pump 932 is attached, either directly or via a length of tubing 954,to the aorta of the person receiving the artificial heart. (For clarityof illustration, the artificial heart 931 has been illustratedschematically such that the pumps 930 and 932 comprising the heart 931are separated from each other. As will be clear to one skilled in theart, the pumps 930 and 932 would be placed in close proximity whenimplanted in the chest cavity of a person receiving the artificial heart931.)

Description of FIG. 38

Referring now to FIG. 38, shown therein is one preferred manner in whicha pump 958, constructed in the manner of the pump 786 illustrated inFIG. 34, is connected to the natural heart 960 to operate as a leftventricular assist device. Such attachment is effected by connecting theoutlet 962 of the pump 958 to the arch of the aorta 964, via a length oftubing 966, and by connecting the inlet 968 of the pump 958 to the leftventricle 970 of the heart 960. For this latter connection, a hole 972would be formed through the wall of the left ventricle so that a lengthof tubing 974 could be sewn to the heart 960 to open into the leftventricle and the tubing 974 would be slipped over the inlet 968 of thepump 958 and secured thereto. Alternatively, the tube 974 can besimilarly sewn to the left atrium.

Although not shown in the Figures, each blood-contacting surface in theapparatus is preferably provided with a continuous, substantially inertcoating, such as that formed by a non-solvent material. One preferredcoating comprises pyrolitic carbon. Among the surfaces which are coatedare the exterior surface of the rotor and the internal bore of thehousing. If desired, non-blood-contacting surfaces, such as the outsideof the housing, may also be coated. The coating protects operativecomponents of the apparatus and, because of its inertness, permitsgreater flexibility in selection of the structural materials from whichblood-contacting components are formed. By using a non-solvent material,it is possible to avoid problems of coating degradation, which are oftenassociated with coatings formed by solution-cast processes.

It is clear that the present invention is well adapted to carry out theobject and attain the ends and advantages mentioned as well as thoseinherent therein. While presently preferred embodiments of the inventionhave been described for purposes of this disclosure, numerous changesmay be made which will readily suggest themselves to those skilled inthe art and which are encompassed within the spirit of the inventiondisclosed and as defined in the appended claims.

What is claimed is:
 1. A pump implantable in the human body to provide areplacement for, or an assist to, the natural heart, comprising:ahousing constructed of or coated with a blood compatible material havingan inlet passage and an outlet passage for connecting the pump into thecirculatory system of the person into which the pump is implanted, thehousing having an impellor chamber fluidly interposed between the inletpassage and the outlet passage; an impellor constructed of or coatedwith a blood compatible material disposed in the housing impellorchamber and rotatable therein about an impellor rotation axis fordrawing blood into the housing inlet passage and discharging blood fromthe housing outlet passage; magnetic suspension means for magneticallysuspending the rotor in said pump chamber out of contact with the wallsof the impellor chamber, comprising:permanent magnet impellor supportmeans comprising an assembly of permanent magnets mounted on theimpellor and on the housing for exerting forces on the impellor tendingto align the rotation axis of the impellor with a selected support axisof the housing while tending to drive the impellor axially away from aselected null position on said support axis at such times that theimpellor is axially displaced from the null position; an electromagnetmounted on the housing and positioned thereon to exert a force directedalong the support axis on portions of the permanent magnet impellorsupport means disposed on the impellor at such times that an electriccurrent is passed through the electromagnet, the electromagnet therebyexerting an axial force on the rotor, electromagnet control meansmounted on the housing for detecting a displacement of the impellor froma control position of the impellor on the support axis and passing acurrent through the electromagnet to drive the impellor toward thecontrol position; and impellor drive means mounted on the housing forsensing a preselected physical quantity related to the flow of blood insaid circulatory system and magnetically coupled to the impellor forrotating the impellor at a rate varying in accordance with a selectedrelationship to the value of said quantity.
 2. The pump of claim 1wherein said physical quantity is the pressure in the inlet passage ofthe housing.
 3. The pump of claim 2 wherein the impellor chamber, theinlet passage and the outlet passage are characterized as being portionsof a bore formed through the housing; wherein an annular restriction isformed in the inlet passage of the pump; and wherein the pump furthercomprises a valve member mounted on the impellor adjacent saidrestriction, the valve member having a nose portion shaped to mate withsaid restriction whereby the inlet passage of the housing can be closedby movement of the valve member nose portion into said restriction. 4.The pump of claim 1 wherein said control position is coincident withsaid null position.
 5. The pump of claim 1 wherein the electromagnetcontrol means is characterized as comprising means for selecting thecontrol position in a displaced relation to the null position along saidsupport axis, whereby the permanent magnet rotor support means willexert a force on the rotor at such times that the rotor is in thecontrol position, thereby enabling the permanent magnets of thepermanent magnet impellor support means to balance a static forceexerted axially on the rotor.
 6. The apparatus of claim 1 in whichblood-contacting surfaces of the housing and rotor are each providedwith a non-solvent coating.
 7. An artificial heart for implantation inthe body of a human subject comprising:a first pump comprising a housingconstructed of or coated with a blood compatible material having aninlet passage fluidly connectable to the subject's left atrium and anoutlet passage fluidly connectable to the subject'aorta; and a secondpump comprising a housing constructed of or coated with a bloodcompatible material having an inlet passage connectable to at least oneof the subject's superior vena cava and inferior vena cava and an outletpassage fluidly connectable to the subject's pulmonary artery;whereinthe housing of each of said pumps has an impellor chamber disposedbetween the housing inlet passage and the housing outlet passage; andwherein each of said pumps further comprises: an impellor disposed inthe housing impellor chamber and rotatable therein about an impellorrotation axis for drawing blood from the housing outlet passage;magnetic suspension means disposed partially on the impellor andpartially on the housing for magnetically suspending the impellor insaid impellor chamber out of contact with the walls of the pump chamber,comprising:permanent magnet impellor means comprising an assembly ofpermanent magnets mounted on the impellor and on the housing forexerting forces on the impellor tending to align the rotation axis ofthe impellor with a selcted support axis of the housing while tending todrive the impellor axially away from a selected null position on saidsupport axis at such times that the impellor is axially displaced fromthe null position; an electromagnet mounted on the housing andpositioned thereon to exert a force directed along the support axis onportions of the permanent magnet impellor support means disposed on theimpellor at such times that an electric current is passed through theelectromagnet, the electromagnet thereby exerting an axial force on therotor; and electromagnet control means mounted on the housing fordetecting a displacement of the impellor from a control position of theimpellor on the support axis and passing a current through theelectromagnet to drive the impellor toward the control position; andimpellor drive means disposed partially on the impellor and partially onthe housing for turning the impellor about said rotation axis, whereinportions of the impellor drive means disposed on the impellor arecoupled solely magnetically to portions of the impellor drive meansdisposed on the housing.
 8. The apparatus of claim 7 in whichblood-contacting surfaces of the housing and rotor are each providedwith a non-solvent coating.
 9. A pump for pumping blood implantable inthe human body to provide a replacement for, or an assist to, thenatural heart, comprising:a housing constructed of or coated with ablood compatible material having an inlet passage and an outlet passagefor connecting the pump into the circulatory system of the person intowhich the pump is implanted, the housing having an impellor chamberfluidly interposed between the inlet passage and the outlet passage; animpellor constructed of or coated with a blood compatible materialdisposed in the housing impellor chamber and rotatable therein about animpellor rotation axis for drawing blood into the housing inlet passageand discharging blood from the housing outlet passage; magneticsuspension means for magnetically suspending the rotor in said pumpchamber out of contact with the walls of the impellor chamber,comprising:permanent magnet impellor support means comprising anassembly of permanent magnets mounted on the impellor and on the housingfor exerting forces on the impellor tending to align the rotation axisof the impellor with a selected support axis of the housing whiletending to drive the impellor axially away from a selected null positionon said support axis at such times that the impellor is axiallydisplaced from the null position; an electromagnet mounted on thehousing and positioned thereon to exert a force directed along thesupport axis on portions of the permanent magnet impellor support meansdisposed on the impellor at such times that an electric current ispassed through the electromagnet, the electromagnet thereby exerting anaxial force on the rotor. electromagnet control means mounted on thehousing for detecting a displacement of the impellor from a controlposition of the impellor on the support axis and passing a currentthrough the electromagnet to drive the impellor toward the controlposition; impellor drive means mounted on the housing for sensing thepressure in the inlet passage of the housing related to the flow ofblood in the circulatory system and magnetically coupled to the impellorfor rotating the impellor at a rate varying in accordance with aselected relationship to the value of the pressure in the inlet passageof the housing; and wherein the combined center of gravity of theimpellor and portions of the impellor drive means and permanent magnetimpellor support means disposed thereon is positioned at the center ofbuoyancy of the impellor, and wherein a cavity is formed in the impellorto match the average specific gravity of the impellor and portions ofthe drive means and the permanent magnet impellor support means thereonto the specific gravity of blood.
 10. A pump implantable in the humanbody to provide a replacement for, or an assist to, the natural heart,comprising:a housing constructed of or coated with a blood compatiblematerial having an inlet passage and an outlet passage for connectingthe pump into the circulatory system of the person into which the pumpis implanted, the housing having an impellor chamber fluidly interposedbetween the inlet passage and the outlet passage; an impellorconstructed of or coated with a blood compatible material disposed inthe housing impellor chamber and rotatable therein about an impellorrotation axis for drawing blood into the housing inlet passage anddischarging blood from the housing outlet passage; magnetic suspensionmeans for magnetically suspending the rotor in said pump chamber out ofcontact with the walls of the impellor chamber, comprising:permanentmagnet impellor support means comprising an assembly of permanentmagnets mounted on the impellor and on the housing for exerting forceson the impellor tending to align the rotation axis of the impellor witha selected support axis of the housing while tending to drive theimpellor axially away from a selected null position on said support axisat such times that the impellor is axially displaced from the nullposition; an electromagnet mounted on the housing and positioned thereonto exert a force directed along the support axis on portions of thepermanent magnet impellor support means disposed on the impellor at suchtimes that an electric current is passed through the electromagnet, theelectromagnet thereby exerting an axial force on the rotor,electromagnet control means mounted on the housing for detecting adisplacement of the impellor from a control position of the impellor onthe support axis and passing a current through the electromagnet todrive the impellor toward the control position; comprising:means forselecting the control position in a displaced relationship to the nullposition along said support axis, whereby the permanent magnet impellorsupport means will exert a force on the impellor at such times that theimpellor is in the control position, thereby enabling the permanentmagnets of the permanent magnet impellor support means to balance astatic force exerted axially on the impellor; impellor drive meansmounted on the housing for sensing a preselected physical quantityrelated to the flow of blood in said circulatory system and magneticallycoupled to the impellor for rotating the impellor at a rate varying inaccordance with a selected relationship to the value of said quantity;and wherein the combined center of gravity of the impellor and portionsof the impellor drive means and permanent magnet impellor support meansdisposed thereon is positioned at the center of buoyancy of theimpellor, and wherein a cavity is formed in the impellor to match theaverage specific gravity of the impellor and portions of the drive meansand the permanent magnet impellor support means thereon to the specificgravity of blood.